Waveplate and optical circuit formed from mesogen-containing polymer

ABSTRACT

Waveplates formed of mesogen-containing polymers and planar lightwave circuits containing such waveplates. Polymers have sidechains containing mesogens such as biphenyl-containing groups. Polymers may have a glass transition temperature between 100 C and 300 C, and polymers may be stretched in excess of 150% to increase birefringence of polymer and provide thin films. Waveplates formed of stretched polymer films may have high biaxial birefringence.

This application claims benefit of U.S. Provisional Application Ser. No.60/329,979, filed Oct. 16, 2001, the contents of which is herebyincorporated by reference into the present application for all purposesas if fully put forth herein.

BACKGROUND OF THE INVENTION

Planar lightwave circuits (PLCs) in telecommunications, such as arrayedwaveguide gratings (AWGs) used to multiplex or demultiplex multipleoptical signals transmitted over a single optical fiber, typically areformed of birefringent materials such as doped SiO₂ or LiNbO₃.Birefringence in planar waveguides complicates the design and operationof PLCs. Planar waveguides as are found in AWGs typically have differentpropagation constants for TE (transverse electric) and TM (transversemagnetic) waveguide modes caused by stress-induced birefringenceintroduced into the waveguides due to mismatched coefficients of thermalexpansion of the substrate, core, and cladding. For AWGs, thisdifference in propagation constants produces a wavelength shift betweeneach AWG channel's peak response to the TE input polarization and thatchannel's response to the TM polarization. The difference between thewavelength of peak TE transmission and the wavelength of peak TMtransmission is called a polarization dependent wavelength shift (PDW).Even a small PDW may be a concern because of the problems it may cause,such as poor channel isolation as well as increasedpolarization-dependent loss (PDL).

One way to compensate for birefringence is to formulate a waveplate of arigid polyimide polymer having a heat resistance of 300° C. or higher,as disclosed in U.S. Pat. No. 6,115,514. The waveplate changes thepolarization state of light passing through the waveplate. The patentexpresses a clear preference that the waveplate is formed of a rigidpolymer with no more than 2 rotatable chemical bonds. The interchainorientation and intermolecular interactions of the polymer backbonescreates birefringence and thermal stability as a sheet of the polymer isuniaxially drawn or stretched. Further, the patent states that it isnecessary for the polymer to have a heat resistance in excess of 300° C.

Another way to compensate for birefringence is to use a birefringentcrystal waveplate. Reported in 1992, a quartz waveplate was used tocorrect for polarization dependence in an arrayed-waveguide grating(AWG) multiplexer, although the method had high loss. More recently, athin (10 μm thick) LiNbO3 half waveplate created using crystal ionslicing was demonstrated that could substantially reduce loss. In thispaper, concerns are expressed about the hygroscopic nature of polyimidesand possible long-term changes due to environmental factors. Inaddition, the LiNbO3 work stated the desire to improve polarization modeconversion ratios and the desire to create thinner waveplates forinsertion loss reduction.

BRIEF SUMMARY OF THE INVENTION

The invention provides a polymeric waveplate and a planar lightwavecircuit (PLC) containing the polymeric waveplate that corrects for orintroduces a desired amount of birefringence into the PLC, creating adesired effect on the polarization state of an optical signal passingthrough the waveplate. The polymeric waveplate is formed of a polymerthat has a mesogen in a side-chain of the polymer. The sidechain has anoptional linker that attaches the sidechain to the polymer backbone andan optional spacer between the linker and the mesogen. The waveplate isformed by creating a thin film of the polymer and then uniaxiallydrawing (stretching) it at an elevated temperature to create therequired degree of birefringence for the waveplate.

Birefringence in polymers can be created by inducing directionalstress/strain in a film. When this directional stress/strain is appliedto a polymer film, interchain orientation can result. The degree oforientation per unit stress/strain, and thus the magnitude of theinduced birefringence, differs for polymers of differing compositions.The rate at which this orientation develops is increased when thepolymer film is above its glass transition temperature. As thetemperature of the film becomes lower than the glass transitiontemperature, some degree of orientation, and thus some level ofincreased birefringence, can be maintained. The degree of orientationthat is maintained is influenced by the ability of the material todevelop intermolecular, interchain interactions above Tg which persistsas the temperature of the material falls below the glass transition.

One way to achieve such interactions is through strong interactionsbetween polymer backbones. Polyimides are a class of materials thatexhibits a degree of intermolecular, interchain interaction, whichresults in superior mechanical and high temperature properties. Thishigh degree of interaction also results in birefringence in stressedpolyimide films. In general, the higher the degree of rigidity of thepolyimide backbone, the higher the degree of interchain interaction andthe lower the achievable elongation upon drawing. In fact, crystallinityhas been observed in the most rigid materials. Species such as flexiblegroups in the backbone and flexible sidechains ordinarily disrupt thedegree of organization that the material can achieve. The presence ofthese moieties is thus ordinarily deleterious to the degree ofbirefringence that can be developed. These observations have beenreported in the '514 patent, which expresses a strong preference formaterials that contain no more than two (2) rotatable (swivel) bonds andthus a minimum degree of flexibility in the backbone. Ordinarily,high-rigidity polyimides such as those in the '514 patent exhibit highmodulus and high glass-transition temperature Tg, and are not readilydrawable to a significant degree. Stress must therefore be developed ina precursor polyamic acid film by drawing or by constraining the filmand relying on shrinkage stress or anisotropic substrate expansion toprovide and/or maintain orientation. The more flexible polymer precursormay then be further reacted, possibly under constraint, to preserveorientation.

It appears that one of the problems associated with waveplates formed ofa high-rigidity polyimide is that the waveplate may be slightly warpedrather than completely flat due to stresses introduced when forming thepolymer into a waveplate. A waveplate formed of a high-rigiditypolyimide can be warped to an extent that a surface of the waveplatestands as much as 1 mm off of a flat, horizontal surface upon which thewaveplate is laid, despite the waveplate being only approximately 25 μmthick.

The polymers of this invention contain mesogenic side chains and areoften composed of a more flexible backbone than the '514 patent teachesare possible if one desires to produce waveplate, and in particular,half waveplate articles. Further, the polymers of this invention can bedrawn at significantly lower processing temperatures due to theflexibility of the backbone and the presence of the sidechains. Althoughthe flexibility of the backbone and presence of side chains reduceinterchain interactions from the polymer backbone itself, the mesogensassociate with one another to provide the necessary additional degree ofinteraction that maintains the order created by the stretching processand enable high birefringence to be attained. Thus the birefringenceachieved during stress/strain above Tg provides a film that is suitablefor use as a waveplate article after cooling and release from astretching apparatus. This is achievable in spite of the presence ofmore flexible bonds than the '514 patent suggests are possible and inspite of the presence of side chains that would ordinarily be regardedas deleterious to the development of interchain interactions and thus tothe development of sufficient birefringence for the production of thinwaveplate articles. The temperature stability of the waveplates producedusing exemplary mesogenic polymers of this invention is suitable for useup to 145 C and reliable performance has been observed after repeateduse at elevated temperature.

The incorporation of mesogenic structures as sidechains is a generalconcept that can, in principle, be applied to a variety of backbonestructures and releases the technology from a reliance on “rigid”backbone materials as defined in the '514 patent. They can be used tocreate high-birefringence films from highly drawable, flexible backbonesthat are less prone to crystallinity and would otherwise be unlikely tobe capable of high birefringence. Although the mesogen itself may inmany embodiments of the invention not appreciably contribute directly tothe birefringence, its main purpose in these embodiments is tosimultaneously aid in the ability to draw (stretch) the polymer attemperatures well below 300° C. and raise the stability of the stretchedstructure through intermolecular interactions. The ability to strain thematerial over a wider range allows the production of birefringentarticles of varying and potentially continuous waveplate performance. Inaddition, the mesogens help to provide low water sensitivity to thepolymer when appropriately chosen.

The polymer may be uniaxially or biaxially drawn, and is preferablyuniaxially drawn to create the birefringence necessary for a waveplate.An exemplary 15 μm thick half waveplate for operation at 1550 nmwavelength requires a birefringence of 0.52. The polymer of theinvention can be cast into a thin film of appropriate thickness greaterthan 15 μm, and drawn to achieve the desired 15 μm thickness and 0.052birefringence. Alternatively, the thickness of the cast film can bechosen such that the film can be drawn to a higher level ofbirefringence to facilitate a half waveplate as thin as 8 μm for thesame application.

When forming a waveplate, the drawability, or ease with which thepolymer can be drawn, is advantageously good, as evidenced by the largeextent to which the polymer may be drawn. For instance, the polymer maybe uniaxially drawn with elongation (localized change in length dividedby original length) in excess of 50%, and is often drawn with elongationon the order of 100%-200%.

A waveplate of the invention preferably has a warpage of less than about350 μm, more preferably less than about 250 μm warpage, and morepreferably still less than about 150 μm warpage. Warpage is measured byplacing the waveplate on a flat, horizontal surface and measuring thedistance from that surface to the highest point on the restingwaveplate.

What is disclosed by way of example and not by way of limitation is:

A waveplate comprising a mesogen-containing polymer film having abackbone and having sidechains containing mesogen groups, wherein themesogen-containing polymer film has a length, a width, and a thicknesssuch that said mesogen-containing polymer film is insertable into achannel in an optical pathway of the planar lightwave circuit.

A waveplate according to paragraph [0014] wherein saidmesogen-containing polymer film has a birefringence sufficiently high torotate or convert a polarization state of an optical signal traversingthe optical pathway.

A waveplate according to paragraph [0015] wherein the birefringence isat least 0.52.

A waveplate according to paragraph [0015] wherein the waveplate is ahalf waveplate of thickness between 5 and 25 μm.

A waveplate according to paragraph [0015] wherein the waveplate is aquarter waveplate of thickness between 5 and 25 μm.

A waveplate according to paragraph [0014] wherein the mesogen-containingpolymer film is formed of a polymer having a glass transitiontemperature between 100 C and 300 C.

A waveplate according to paragraph [0014] wherein the backbone containsmonomers having at least two groups that provide rotational freedomwithin the backbone.

A waveplate according to paragraph [0014] wherein the waveplate has awarpage of less than 350 μm.

A waveplate according to paragraph [0014] wherein the backbone comprisesa polymer selected from the group consisting of: polyimides,polyetherimides, polyesterimides, polyamideimides, polyketones,polyarylethers, polyetherketones, polysulfones, polysulfides,polyarylenes, polyesters, polyamides, polycarbonates, polyolefins,polyvinylesters, polyurethanes, polyacrylates, polyphenylenes.

A waveplate according to paragraph [0022] wherein the backbone comprisespolyetherimide polymer.

A waveplate according to paragraph [0022] wherein the backbone comprisespolyamide polymer.

A waveplate according to paragraph [0023] wherein the backbone is formedof one or more components selected from the group consisting of4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride);4,4′-(hexafluoroisopropylidene) diphthalic anhydride;2,2′-bis(trifluoromethyl)benzidine; andbis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate.

A waveplate according to paragraph [0024] wherein the backbone is formedof one or more components selected from the group consisting ofisophthalic chloride; 2,2′-bis(trifluoromethyl)benzidine;bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate; and4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride).

A waveplate according to paragraph [0026] wherein the backbone is formedof isophthalic chloride; 2,2′-bis(trifluoromethyl)benzidine; andbis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate.

A waveplate according to paragraph [0026] wherein the backbone is formedof 2,2′-bis(trifluoromethyl)benzidine;bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate; and4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride).

A waveplate according to paragraph [0014] wherein the mesogen groupshave the form phenyl-X-phenyl-R or phenyl-phenyl-R, where X is selectedfrom the group consisting of azo, diazo, azoxy, nitrone, carbon-carbondouble bond, carbon-carbon triple bond, amide, imide, Schiff base, andester; and R is selected from the group consisting of poly(alkyleneoxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphaticpolyether.

A waveplate according to paragraph [0014] wherein the mesogen groups areselected from the group consisting of trans 1,3 cyclohexane; trans 1,4cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.

A waveplate according to paragraph [0022] wherein the mesogen groupshave the form phenyl-X-phenyl-R or phenyl-phenyl-R, where X is selectedfrom the group consisting of azo, diazo, azoxy, nitrone, carbon-carbondouble bond, carbon-carbon triple bond, amide, imide, Schiff base, andester; and R is selected from the group consisting of poly(alkyleneoxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphaticpolyether.

A waveplate according to paragraph [0022] wherein the mesogen groups areselected from the group consisting of trans 1,3 cyclohexane; trans 1,4cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.

A waveplate according to paragraph [0014], [0022], [0023], or [0024]wherein the mesogen group is biphenyl.

A waveplate according to paragraph [0014] wherein the mesogen groupscomprise at least two aromatic groups and wherein the mesogen groupsassociate to help maintain birefringence as the film is drawn.

A waveplate according to paragraph [0014] wherein the side chainscomprise linking groups linking the mesogen groups to the backbone,wherein the linking groups are selected from the group consisting of:ether, ester, amide, imide, urethane, alkylene, alkyl.

A waveplate according to paragraph [0022] wherein the side chainscomprise linking groups linking the mesogen groups to the backbone,wherein the linking groups are selected from the group consisting ofether, ester, amide, imide, urethane, alkylene, alkyl.

A waveplate according to paragraph [0029] wherein the side chainscomprise linking groups linking the mesogen groups to the backbone,wherein the linking groups are selected from the group consisting ofether, ester, amide, imide, urethane, alkylene, alkyl.

A waveplate according to paragraph [0030] wherein the side chainscomprise linking groups linking the mesogen groups to the backbone,wherein the linking groups are selected from the group consisting ofether, ester, amide, imide, urethane, alkylene, alkyl.

A waveplate according to any of paragraphs [0014], [0022], [0029],[0030], and [0034]-[0038] wherein the side chains further comprisespacing groups linking the mesogen groups to the linking groups, thespacing groups being selected from the group consisting of poly(alkyleneoxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphaticpolyether.

A waveplate according to paragraph [0014] wherein the spacing groups aresufficiently long and sufficiently flexible to allow the mesogens ofadjacent sidechains to associate as a film of the mesogen-containingpolymer is stretched.

A planar lightwave circuit comprising a waveguide and a waveplateaccording to any of paragraphs [0014]-[0040] positioned in an opticalpathway of the waveguide.

A planar lightwave circuit according to paragraph [0041] wherein thewaveplate is a half waveplate.

A planar lightwave circuit according to paragraph [0041] wherein thewaveplate is a quarter waveplate.

A planar lightwave circuit according to paragraph [0041] wherein thewaveplate resides in a channel cut or etched through the waveguide.

A planar lightwave circuit according to paragraph [0041] wherein thewaveguide is one of a plurality of waveguides of an arrayed waveguidegrating positioned between two free propagation regions of the planarlightwave circuit, and wherein the waveplate is positioned in an opticalpathway of each of the plurality of waveguides of the arrayed waveguidegrating.

A planar lightwave circuit according to paragraph [0041] wherein thewaveguide is positioned at an angle to the waveguides that reduces backreflection caused by the waveplate groove, glue, and waveplate.

A method of making an optical device comprising

-   -   (a) providing a mesogen-containing polymer film; and    -   (b) forming the mesogen-containing polymer piece to have a        length, a width, and a thickness adapted for use in a planar        lightwave circuit, the mesogen-containing polymer piece having a        birefringence not equal to zero, said birefringence being        suitable for use in a waveguide of a planar lightwave circuit

A method according to paragraph [0047] and further comprising insertingthe polymer piece into an optical pathway of a waveguide of the planarlightwave circuit.

A method according to paragraph [0047] wherein the mesogen-containingpolymer film has a polymer backbone selected from the group consistingof polyimides, polyetherimides, polyesterimides, polyamideimides,polyketones, polyarylethers, polyetherketones, polysulfones,polysulfides, polyarylenes, polyesters, polyamides, polycarbonates,polyolefins, polyvinylesters, polyurethanes, polyacrylates,polyphenylenes.

A method according to paragraph [0047] wherein the mesogen-containingpolymer film contains at least one mesogen having the formphenyl-X-phenyl-R or phenyl-phenyl-R, where X is selected from the groupconsisting of azo, diazo, azoxy, nitrone, carbon-carbon double bond,carbon-carbon triple bond, amide, imide, Schiff base, and ester; and Ris selected from the group consisting of poly(alkylene oxide),polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.

A method according to paragraph [0047] wherein the mesogen groups areselected from the group consisting of trans 1,3 cyclohexane; trans 1,4cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.

A method according to paragraph [0051] wherein the mesogen-containingpolymer film contains at least one mesogen having the formphenyl-X-phenyl-R or phenyl-phenyl-R, where X is selected from the groupconsisting of azo, diazo, azoxy, nitrone, carbon-carbon double bond,carbon-carbon triple bond, amide, imide, Schiff base, and ester; and Ris selected from the group consisting of poly(alkylene oxide),polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.

A method according to paragraph [0051] wherein the mesogen groups areselected from the group consisting of trans 1,3 cyclohexane; trans 1,4cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.

A method according to paragraph [0047] wherein the mesogen-containingpolymer film has at least one linking group selected from the groupconsisting of ether, ester, amide, imide, urethane, alkylene, alkyl.

A method according to paragraph [0051] wherein the mesogen-containingpolymer film has at least one linking group selected from the groupconsisting of ether, ester, amide, imide, urethane, alkylene, alkyl.

A method according to paragraph [0052]wherein the mesogen-containingpolymer film has at least one linking group selected from the groupconsisting of ether, ester, amide, imide, urethane, alkylene, alkyl.

A method according to paragraph [0053] wherein the mesogen-containingpolymer film has at least one linking group selected from the groupconsisting of ether, ester, amide, imide, urethane, alkylene, alkyl.

A method according to paragraph [0054] wherein the mesogen-containingpolymer film has at least one linking group selected from the groupconsisting of ether, ester, amide, imide, urethane, alkylene, alkyl.

A method according to paragraph [0055] wherein the mesogen-containingpolymer film has at least one linking group selected from the groupconsisting of ether, ester, amide, imide, urethane, alkylene, alkyl.

A method according to any of paragraphs [0047] and [0051]-[0061] whereinthe mesogen-containing polymer film has at least one spacer groupselected from the group consisting of poly(alkylene oxide), polyalkane,polyperfluoroalkane, polysiloxane, and aliphatic polyether.

A method of using a mesogen-containing polymer, said method comprisingprocessing the mesogen-containing polymer into a film with birefringencein the plane of the film, inserting the mesogen-containing polymer filminto an optical pathway of a waveguide of a planar lightwave circuitsuch that the polymer effects a change in an optical signal transmittedthrough the waveguide and the polymer.

A method of using a mesogen-containing polymer comprising passing anoptical signal having a first polarization state through a waveguide andthe polymer such that the optical signal has a second polarization statenot identical to the first polarization state.

Among other factors, the invention is based in the technical findingthat a preferred polymer formed of a flexible polymeric backbone havinga mesogen attached to the backbone through a linker and a spacer can bedrawn uniaxially to provide a thin preferred waveplate (typically lessthan 20 μm thick) that is flat and can be inserted into a planarlightwave circuit while the intermolecular interactions enhanced by themesogens maintain sufficiently high birefringence in the stretchingprocess to allow the waveplate to compensate for polarization effectscreated by birefringence elsewhere in the PLC. Such preferred polymer isdrawn in a single step at temperatures well below 300° C., and can bedrawn up to in excess of 150% to achieve high birefringence up to inexcess of 0.1 with a high degree of repeatability and uniformity. Themesogen helps maintain the birefringence created in drawing as long asthe waveplate is operated sufficiently below the Tg of the polymer. Themesogen of the preferred waveplate also acts much as an internalplasticizer acts, reducing the glass-transition temperature (Tg) so thatthe fully-reacted polymer can be reliably and repeatably drawn to formthe waveplate without need for further reacting of the polymer (such asimidization) during or after drawing, and without need for appreciablesolvent content in the film. These technical findings and advantages andothers are apparent from the discussion herein.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph of birefringence as a function of the local elongation(localized change in length divided by original length) for an exemplarymaterial.

FIG. 2 shows the thickness of a half waveplate and a quarter waveplatemade from the material of FIG. 1, as a function of the local elongation.

FIG. 3 is a graph of birefringence as a function of the local elongation(localized change in length divided by original length) for anotherexemplary material.

FIG. 4 shows the thickness of a half waveplate and a quarter waveplatemade from the material of FIG. 3, as a function of the local elongation.

FIG. 5 is a graph of the calculated insertion loss due to a waveplategroove as a function of the groove width.

FIG. 6 depicts monomers used to form a mesogen-containing polyetherimidepolymer and the resultant polymer that can be used in optical devices ofthe invention.

FIG. 7 depicts monomers used to form a mesogen-containing polyamidepolymer and the resultant polymer that can be used in optical devices ofthe invention.

FIG. 8 illustrates a PLC of the invention, an arrayed waveguide grating.

FIG. 9 illustrates another PLC of the invention, a wavelength divisionmultiplexer based on a Mach-Zehnder interferometer.

FIG. 10 depicts a set of reactions to form a monomer used in forming thepolymer depicted in FIG. 6.

FIG. 11 depicts an additional set of reactions to form another monomerused in forming the polymer depicted in FIG. 7.

FIG. 12 depicts monomers used to form a mesogen-containing polyamidepolymer and the resultant polymer that may be useful in optical devicesof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A waveplate of the invention formed of a mesogen-containing polymer isuseful in compensating for birefringence in a planar lightwave circuit(PLC). A PLC typically is formed of a birefringent material such asdoped silicon oxide or lithium niobate, such that the transverseelectric (TE) and transverse magnetic (TM) modes of the optical signaltravel at different velocities through the material and arrive at agiven part of the PLC or a detector integrated into the PLC out ofphase. In many instances, a thin half waveplate inserted into theoptical path of the PLC with its principle axis oriented at 45° to theplane of the PLC compensates for problems generated by birefringence inany part of the PLC. Thus, the TE and TM modes arrive at the desiredpart of the PLC within a period of time of each other that allows thePLC to function independently of input polarization without having toitself compensate for the birefringence.

In practical PLC devices made from practical PLC materials such as dopedsilicon oxide, polymers, silicon oxide and polymers, or lithium niobate,TE and TM modes of an optical signal can also experience differing lossof intensity through the components of a PLC device such as waveguides,couplers, star couplers, and waveguide gratings. This loss difference iscalled polarization dependent loss (PDL), and is preferably minimized,most preferably zero, although in practical PLC devices, the PDL can beunacceptably large. In many instances, a thin half waveplate insertedinto the optical path of the PLC with its principle axis oriented at 45°to the plane of the PLC compensates for PDL by causing equivalent lossesfor light entering the waveguide in TE and TM modes.

Cutting a groove in a PLC and inserting the waveplate in the PLC causesundesirable additional loss, termed insertion loss, of the light in thePLC. The loss occurs when light in a waveguide reaches the groove andwaveplate, and rapidly spreads by diffraction. When it reaches thewaveguide on the other side of the groove, not all the light can make itback into the single-mode waveguide. A groove made wider to accommodatea wider waveplate will have higher loss, thus a narrower groove (andthus narrower waveplate) are preferable. FIG. 5 shows the theoreticalinsertion loss caused by a waveplate groove as a function of the groovewidth. This additional insertion loss decreases with decreasing width ofthe groove into which the waveplate is inserted, which is typically 2-10μm wider than the thickness of the waveplate. Thus it is desirable tohave a waveplate of a minimal practical thickness to allow a groove ofminimum practical thickness which in turn gives the minimum practicalinsertion loss. For this reason, the waveplate is typically made quitethin, being less than 30 μm, preferably less than about 20 μm, and morepreferably less than 15 μm thick.

Further, as mentioned above, preferred waveplates of this invention havelittle warpage. A flat waveplate requires a thinner channel forinsertion into a PLC than does a warped waveplate. Oftentimes it isextremely difficult to insert a warped waveplate, especially one made ofa rigid polyimide, into a channel cut in a PLC to have about the samethickness as the waveplate polymer. It sometimes can be necessary toform a channel of greater width than would be formed for a flatwaveplate to allow a warped waveplate to be inserted into the channelwithin a reasonable period of time. A flat waveplate as provided incertain embodiments of this invention can therefore aid in reducinginsertion loss, since the channel in the PLC into which the waveplate isinserted can be formed only about 2-5 μm wider than the waveplatethickness.

Polymers typically have a much lower transmittance of optical power perunit thicknesss than waveguides made of inorganic materials such as SiO₂or LiNbO₃ as found in many PLCs (especially those of the invention).Consequently, thin polymeric waveplates made using a mesogen-containingpolymer often transmit more optical power than do thicker polymericwaveplates. Additionally, the use of mesogens allows more flexibility inselecting a polymer backbone with low optical absorption.

The most commonly used waveplates in PLC devices are quarter and halfwaveplates for use at the common optical communication wavelengths of1300 nm and 1550 nm. Examples of waveplates that may be used with PLCdevices include a 7.5 μm thick quarter waveplate at 1300 nm (requiring abirefringence of 0.043), a 7.5 μm thick quarter waveplate at 1550 nm(requiring a birefringence of 0.052), a 15 μm thick half waveplate at1550 nm (requiring a birefringence of 0.052), and a 10 μm half waveplateat 1550 nm (requiring a birefringence of 0.078). A polymer for use inmaking waveplates therefore is preferably capable of reaching orexceeding a birefringence when drawn of 0.043, more preferably 0.052,and even more preferably 0.078.

A mesogen-containing polymer is made into a waveplate by drawing(stretching) and heating a thin film of the polymer that starts withlittle or no in-plane birefringence. The birefringence of the polymerfilm used to make the waveplate may be achieved by stretching eitheruniaxially and/or biaxially by any method known to one of ordinaryskill. A mesogen-containing polymer often increases in birefringence asthe polymer is drawn. The mesogens align and associate during thedrawing process to maintain sufficient birefringence in the flexiblefilm to rotate polarization or convert from one form of polarization toanother (such as from linear to circular), for instance. An exemplarymesogen-containing polymer of this invention is presented later in whichthe maximum attained birefringence upon drawing is greater than 0.105.Such a polymer can be drawn less than this maximum amount to achieve thenecessary birefringence of 0.052 to make a 15 μm half waveplate for useat 1550 nm wavelength, for example.

Most often a ½ waveplate or a ¼ waveplate is used. However any valuebetween 0 and 1 or more waves is often obtainable with amesogen-containing polymer. For example, the waveplate may differ fromthese established values by a small amount to allow the waveplate to beinserted into a PLC at an angle slightly different from perpendicular tothe direction of light propagation such that the light in the waveguideexperiences the desired effect.

The waveplate may be a transmissive waveplate, in which an opticalsignal exits a face opposite to the face of the waveplate that thesignal entered. Alternatively, the waveplate may be a reflectivewaveplate, in which one face of the waveplate is coated with areflective substance such as gold, sliver, aluminum, copper, palladium,nickel, or titanium by sputter-coating a stretched polymer film prior toforming the waveplate. The reflective coating reflects an optical signalback through the polymer film through which it traveled to reach thecoating, allowing the polymer film to be only half as thick as wouldotherwise be needed to effect a desired change in an optical signal.

The polymer used to form the waveplate has a mesogen attached to apolymeric backbone by a linker and an optional spacer. This generalconfiguration is also found in side chain polymer liquid crystals, andmany polymers suitable to form side chain polymer liquid crystals can beused as the basis to form waveplates and PLCs of the invention byforming the polymer to have a suitable molecular weight and by reducingthe number of mesogen groups present on a polymer molecule so that thepolymer does not form large liquid crystal phases that would otherwisediffract or block light from passing through the polymer.

Each of the components of the polymer is discussed in turn.

Mesogen

As a film of mesogen-containing polymer is drawn, the mesogens associateto maintain the birefringence after the film is drawn. The mesogen maybe any single or combination of mesogens used in making liquid crystalpolymers. Thus, usually the mesogen is made up of a rigid core of one ormultiple aromatic rings.

A mesogen as used in the waveplate or PLC of the invention may be acompound as depicted in Formula 1 and/or Formula 2:-phenyl-phenyl-R  Formula 1-phenyl-X-phenyl-R  Formula 2where X is any rigid central linkage that keeps one phenyl group in afixed spatial relationship with the other phenyl group to which it isattached, including azo, diazo, nitrone, azoxy, carbon-carbon doublebond (to give stilbene), carbon-carbon triple bond (to give tolan),amide, imide, Schiff base, and ester; and R is a substituent such ashydrogen or a flexible spacer such as an alkyl, cycloalkyl, aryl,aralkyl, alkaryl, cyano, alkoxy, acyloxy, or halogen. Examples of thesegroups are listed in Table 1.

Preferred mesogens include:

-   phenyl-phenyl (R is hydrogen)-   phenyl-phenyl-cyano-   phenyl-phenyl-acyloxy-   phenyl-phenyl-alkyl (length 1-18 carbons)-   phenyl-phenyl-aryl-   phenyl-C double bond C-phenyl (R is hydrogen)-   phenyl-C double bond C-phenyl-cyano-   phenyl-C double bond C-phenyl-acyloxy-   phenyl-C double bond C-phenyl-alkyl (length 1-18 carbons)-   phenyl-C double bond C-phenyl-aryl-   phenyl-C triple bond C-phenyl (R is hydrogen)-   phenyl-C triple bond C-phenyl-cyano-   phenyl-C triple bond C-phenyl-acyloxy-   phenyl-C triple bond C-phenyl-alkyl (length 1-18 carbons)-   phenyl-C triple bond C-phenyl-aryl-   phenyl-ester-phenyl (R is hydrogen)-   phenyl-ester-phenyl-cyano-   phenyl-ester-phenyl-acyloxy-   phenyl-ester-phenyl-alkyl (length 1-18 carbons)-   phenyl-ester-phenyl-aryl-   phenyl-amide-phenyl (R is hydrogen)-   phenyl-amide-phenyl-cyano-   phenyl-amide-phenyl-acyloxy-   phenyl-amide-phenyl-alkyl (length 1-18 carbons)-   phenyl-amide-phenyl-aryl-   phenyl-azo-phenyl (R is hydrogen)-   phenyl-azo-phenyl-cyano-   phenyl-azo-phenyl-acyloxy-   phenyl-azo-phenyl-alkyl (length 1-18 carbons)-   phenyl-azo-phenyl-aryl

In addition to the forms specified by Formula 1 and Formula 2 above,mesogens may include other ring structures that associate with oneanother with an affinity similar to the structures above, such as trans1,3 cyclohexane; trans 1,4 cyclohexane; trans 2,5 disubstituted 1,3dioxane; trans 2,5 disubstituted 1,3 dithiane; and trans 2,5disubstituted 1,3 dioxathiane.

In a liquid crystal polymer, the mesogens attached to the polymerbackbone are found in one layer, and the polymer backbones localize inanother layer characteristic of the smectic phase. This may in certaininstances help to form a double-comb structure where side chains pointaway from the backbone in an alternating manner.

In a polymer of the invention, it is believed that no appreciablesmectic phase is formed, although birefringence does increase as apolymer film is stretched. It is believed that some mesogens on polymerbackbones may align with one another, but the extent to which suchalignment occurs is either insufficient to form separate phases in thepolymer or, if separate phases form, the extent to which the separatephases are present is not so great that the optical signal is scatteredor lost to the extent that occurs in liquid crystal polymers. Themesogen is present in an amount sufficient to maintain a desiredbirefringence in the waveplate as the polymer is stretched to form afilm of a thickness suitable to form the waveplate.

The polymer has a sufficient number of mesogen groups present in it toprovide a birefringent film that can be formed into a waveplate bydrawing at reasonable temperature as described herein. The polymer mayhave a single mesogen or multiple mesogens per repeating unit of thepolymer, although generally the polymer has fewer than one mesogen perrepeating unit on average. Generally, from about 5 to about 75% of themonomers (mole/mole) have a mesogen attached, preferably from about 10to about 50% of the monomers have a mesogen attached to them. In anexemplary polymer of this invention, two mesogens are attached to one ofevery five repeat units of the backbone.

The mesogen-containing polymer may be a random polymer, in which casemesogen groups are distributed randomly along the polymer.Alternatively, the mesogen-containing polymer may be a block copolymerhaving mesogen groups deliberately clustered together in one or moresegment(s) of the polymer chain.

Polymer Backbone

The polymeric backbone may be a linear polymer such as a polymer formedof one or more of the following monomers or repeating units: olefin,etherimide, ester, vinyl ester, urethane, amide, imide, amide imide,ester imide, acrylate, etherketone, aryl ether, carbonate, sulfone, andphenylene. The linear chains of the polymer backbone may slide past oneanother to some degree to allow the polymer to be stretched along one ormore axes. The mesogens also promote slippage of polymer chains past oneanother, since the mesogens and their optional spacers help to separatepolymer chains and may reduce substantial entanglements that wouldotherwise limit stretching. Backbone polymers may be chosen to providethe desired degree of thermal stability. Preferable backbone polymersinclude polyimides, polyetherimides, polyesterimides, polyamideimides,polyketones, polyarylethers, polyetherketones, polysulfones, aromaticpolysulfides, polyarylenes, aromatic polyesters, aromatic polyamides,and aromatic polycarbonates.

Polymers used to form the waveplate preferably have at least two swivelbonds per repeat unit incorporated into the backbone that allow portionsof the backbone to rotate relative to one another. The polymer can bemade flexible and can be drawn to a large extent due at least in part tothese groups. Such groups include single-bonded carbon, nitrogen,oxygen, sulfur, silicon, and other such groups well-known in the art.

One particularly preferred backbone polymer is a polyetherimide. Apolyetherimide is a flexible polymer because the ether linkages allowthe groups to which the ether linkage is attached to rotate or assumemany different positions. It is believed that a polyetherimide has adegree of movement in the backbone that permits the mesogens toassociate with one another to maintain birefringence, especially as afilm of the polymer is stretched.

Optional Linker

An attachment group, or linker, is any group that permits the mesogen tobe attached to the polymer backbone. A polymer formed of an acrylate orvinyl acetate attaches the mesogen to the hydrocarbon through the esterof the acrylate or acetate groups, respectively. In this instance, theethylene unit of the vinyl acetate or acrylate will be part of thebackbone. The mesogen may be attached directly to the linker, or themesogen may be attached to a spacer that is itself attached to thelinker. Suitable linkers include ester, ether, imide, amide, urethaneand saturated or unsaturated aliphatic groups as described below forspacers. Preferred linkers include esters, ethers, amides and alkylenes.

Optional Spacer

The spacer is an optional group that allows the mesogens to movesomewhat independently of the polymer backbone. The spacer and linkertogether have a length that allows the mesogen to associate with anothermesogen attached to the same polymer backbone and/or to a differentpolymer backbone. Thus, mesogens may associate with one another despitepolymer chain entanglement or lack of polymer backbone orientation alongany one general direction, and the spacer in a polymer can also help toprovide an additional degree of sidechain mobility and placement inconjunction with backbone movement aided by groups that do notsterically hinder portions of the backbone from moving relative to oneanother. Further, a longer spacer helps to reduce the glass transitiontemperature and aid in drawability of a polymer film.

Thus, it is beneficial to have a spacer that is sufficiently long andflexible to allow mesogens on the same and/or adjoining polymers toassociate with one another, especially as a film of the polymer isdrawn. It is also beneficial to have a spacer that is not so shortand/or rigid that a substantial number of mesogens that have associatedare drawn away from each other, substantially reducing or eliminatingthe effect of the mesogens on birefringence. The spacer should not be solong that its properties become significant and affect or even dominatethe properties of the backbone.

Suitable spacers include saturated or unsaturated aliphatic groups,aliphatic polyethers, siloxanes, aliphatic polyesters, aliphaticpolyamides, or other chain-like groups that space the mesogen away fromthe polymer backbone. Aliphatic spacers typically contain from one totwenty carbon atoms (e.g. methyl to didecyl), preferably from two to tencarbon atoms (e.g. ethyl to decyl), and more preferably from four to 10carbon atoms (e.g. butyl to decyl). Preferred spacers include saturatedaliphatic polyether chains having from 3 to 12 carbon atoms such aspolyethylene or polypropylene oxides. Other spacers having about thesame lengths as specified above are also preferred. Other preferredspacers include polyalkylenes having from 2 to 12 carbon atoms,polyperfluoroalkylenes having from 2 to 12 carbon atoms, andpolysiloxanes having from 2 to 12 silicon atoms.

Further Discussion of the Polymer

The polymer is preferably amorphous or substantially amorphous so thatan optical signal passes through the waveplate without a degree ofattenuation or scattering that degrades the performance of the PLCoptical device (such as substantially increasing optical loss) or causesproblems in detecting the optical signal with detection equipment (suchas optical sensors) positioned downstream of the polymer.

A waveplate or PLC in use may experience an elevated temperature for anextended period of time. Typically, these components are housed withinenclosures that contain heat-generating electronic equipment, and oftenthe components are located where cooled air cannot be provided to thecomponents (such as in a pedestal in a residential or business districtlocated in a desert). A PLC for telecommunications application istypically required to operate without failure in ambient environmentswith temperatures as high as 70° C. In some cases, such as most AWG's,the PLC is temperature stabilized at a temperature above this maximumambient temperature to avoid unwanted temperature fluctuations. Thisstabilization temperature typically is at or below 85° C. Thus it isdesirable that any waveplate used in a PLC can be subject to 85° C.temperature for the lifetime of the PLC without degradation in theoptical performance of the waveplate. As the temperature of a polymerwaveplate gets near (within about 10-20° C.) the glass transitiontemperature of the polymer, a process called relaxation occurs, in whichthe heat causes a transition from a glassy state to a more liquid state.This enables motion of the polymer chains and reduces or eliminates theorientation imparted by the strain/stresss, degrading its opticalperformance. As a rule of thumb, a polymer waveplate should be able towithstand temperatures about 40° C. below the polymer's glass transitiontemperature without degradation of optical properties, and higher glasstransition temperatures will mean increased resistance to heat.Therefore, the glass transition temperature of the polymer is preferablyat least about 125 C, and more preferably at least about 150 C. A glasstransition temperature as specified helps to assure that the opticalproperties of the waveplate or PLC do not degrade substantially over aperiod of years by assuring that the polymer does not “melt” or haveareas which undergo a phase transition that can allow polymer moleculesto move relative to one another, potentially changing the birefringence.

The polymer used to make a waveplate or PLC of the invention ispreferably selected to have a glass transition temperature of no morethan about 300 C, and preferably the glass transition temperature is nomore than about 250 C. Such polymer is easy to process into waveplatesreliably and repeatably, without degrading the polymer itself. A polymerwith a glass transition temperature of at least 300 C is more difficultto stretch repeatably and controllably, especially where the polymer isundergoing a polymerization reaction such as imidization simultaneouslywith stretching. The preferred polymer used in waveplates and PLCs ofthe invention is completely reacted (e.g. imidized) prior to stretching,and since the glass transition temperature is less than 300 C for thispolymer, polymer stretching can be controlled easily, and birefringenceis repeatable each time a film of material is stretched.

Mesogens and any associated spacers typically act as a plasticizer toreduce the glass transition temperature of the waveplate polymer andtherefore decrease the temperature required for drawability of thepolymer (especially when attached to the backbone through an optionallinking group). Consequently, in many instances the backbone portion ofthe waveplate polymer may be formed of a polymer that has a high glasstransition temperature and/or is more difficult to draw in the absenceof mesogens, and the incorporation of mesogens into the polymer reducesthe glass transition temperature to below the preferred maximum glasstransition temperature and/or improves drawability.

A polymer used to form a waveplate or PLC of the invention preferablycan be stretched to a sufficient elongation at conveniently achievabletemperatures to achieve the desired birefringence without tearing ordegrading.

Preferably, when compared to a non-mesogen-containing but otherwiseidentical polymer, the mesogen-containing polymer used to form awaveplate or PLC of the invention has a reduced glass-transitiontemperature and improved drawability at a given temperature (as measuredby the amount a polymer film can be stretched without tearing the film).Preferably, it will also have increased birefringence across the planeof the film upon uniaxially drawing a film. Often the birefringence of afilm increases approximately linearly with increase in length duringstretching as illustrated in FIG. 1 (presumably as increased stretchingleads to increased molecular chain alignment while mesogens interact andhelp maintain alignment), and often the increase in birefringence beginsto level off as the film is stretched to high degrees of elongation. Themesogen-containing polymer also preferably may be drawn at a temperatureless than 300 C, which aids in processing the film without degrading it.In fact, the temperature at which the mesogen-containing polymer may bedrawn is often less than the glass transition temperature for thenon-mesogen-containing but otherwise identical polymer.

One knowledgeable in the art will understand that the polymer must havesufficiently high molecular weight to allow the necessary mechanicalstability to be handled as a thin film, and subsequently stretched to asufficient birefringence without breaking or tearing. The birefringenceattainable by a film generally increases with increasing molecularweight (although this increase levels off for higher molecular weights),so a polymer of this invention must be made with sufficiently highmolecular weight to achieve the necessary birefringence for a waveplate.The molecular weight is preferably greater than 30,000 to 100,000,depending on the polymer backbone, and is preferably not so high thatthe polymer becomes impractical to coat into a thin film and/or draw toachieve high birefringence.

The polymer side-chain formed of the mesogen, linking group, andoptional spacer preferably aids in dissolving the polymer in a widerange of solvents. Although the specific solvents depend largely on thebackbone, mesogens usually broaden the range of solvents that can beused, often facilitating solubility in solvents such as ethers, ketones,esters, and chlorocarbons as well as the aprotic solvents such asN-methyl pyrrolidone which are required for rigid polyimides. Thisproperty allows a high-quality thin film to be easily cast from thesolution using well-known solution-based thin-film coating methods suchas spin coating, which film can be further stretched to induce in-planebirefringence prior to forming one or more waveplates of the inventionfrom the film.

In the '514 patent, it is stressed that the polymer must be very rigid,and a strong preference is expressed for polymers that have no more thantwo rotatable bonds (swivel bonds) per repeat unit. However, in theseveral examples in which even two swivel bonds exist, the polymer isnot capable of sufficient birefringence to make a waveplate.

A polymer used to form a waveplate or PLC of the invention is preferablyformed to have at least three swivel bonds per repeating unit of thebackbone that permit portions of the backbone to rotate relative to oneanother. Preferably, the polymer has at least four such bonds, morepreferably five, and even more preferably six. For example, apolyetherimide as shown in FIG. 6 has two swivel bonds in each of thetwo ether linkages plus two swivel bonds in the isopropylidene linkage,giving a total of six swivel bonds in a repeating unit of the backboneabout which portions of the backbone may rotate. For this polymer, arepeat unit is defined herein as the bis-ADA linked to C6BP (thebiphenyl moiety having mesogenic side-chains) or the bis-ADA linked toPFMB (the 2,2′-bis(trifluoromethyl)biphenyl moiety).

The spacers in the sidechains of this polymer are also preferably quiteflexible, having numerous points about which the rigid mesogens (e.g.the biphenyl groups of the side chains illustrated in FIG. 6) mayrotate. In the polymer illustrated in FIG. 6, a biphenyl group mayrotate as a unit about the oxygen atom to which it is attached. Theoxygen atoms and methylene units of sidechains are free to move aboutadjacent methylene units, and the methylene units closest to thebackbone are free to rotate about the oxygen atoms of the esters towhich the methylenes are attached. The sidechains have a high degree offlexibility, and consequently the sidechains can flex and move to allowthe mesogens to associate. Because the mesogens are similar or identicalin structure as well as properties and because the mesogens aresignificantly different in structure and properties from e.g. the spacerand the backbone, it is believed that the mesogens associate to formmicrodomains within the polymer.

In addition to the presence of the mesogens, the polymer may be furthersubstituted or unsubstituted. If substituted, the substituentspreferably do not hinder the film from becoming more birefringent whendrawn. Typical substituents include groups such as alkyl, alcoxy, aryl,aralkyl, ester, cyano, nitro, or halogens such as chlorine or fluorine.The backbone, linker, spacer, and/or mesogen may be substituted.

One particularly preferred polymer is:

-   -   (bis-ADA)₀₅(PFMB_(y)C6BP_(1−y))₀₅,        where y is a number between 0 and 0.25, inclusive. Bis-ADA is        4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride)        represented by the following formula:        and PFMB is 2,2′-bis(trifluoromethyl)benzidine represented by        the following formula:        and C6BP (also known as C6PH) is        bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate        represented by the following formula:

The polymer is a random copolymer, in which the C6BP moiety isdistributed randomly along the polymer. A particularly preferred polymerfor use is that described by the formula above where y=0.2, asrepresented in FIG. 6.

Another particularly preferred polymer is the random copolymer:

-   -   (bis-A_(1−x)6FDA_(x))_(0.5)(PFMB_(y)C6BP_(1−y))_(0.5)        where x is a number between 0 and 0.5, inclusive, and y is a        number between 0 and 0.25, inclusive. A particularly preferred        polymer for use is that described by the formula above, where        x=0.1 and y=0.2. 6FDA is 4,4′-(hexafluoroisopropylidene)        diphthalic anhydride represented by the following formula:

Another particularly preferred polymer is:

-   -   (PFMB_(0.5)IPC_(0.5))_(x)(C6BP_(0.5)IPC₀₅)_(y)        where y is a value between 0.05 and 0.5 and x=1−y. IPC is        isophtlatic chloride represented by the following formula:

This produces a polyamide random copolymer. A particularly preferredpolymer for use is that described by the formula above, where x=0.8 andy=0.2, as illustrated in FIG. 7.

Another polymer that may be useful in the practice of the invention is:

-   -   (PFMB₀₅TPA_(0.5))_(x)(C6BP₀₅TPA_(0.5))_(y)        where y is a value between 0.05 and 0.5 and x=1−y. TPA is        terephthalic acid represented by the following formula:

This produces a polyamide random copolymer as illustrated in FIG. 12.

This same polymer can also be made using terephthalic chloride (TCA)instead of TPA, with reaction conditions modified accordingly. TCA isterephthalic chloride represented by the following formula:

Another polymer that may be useful in the practice of the invention is:

-   -   (PFMB_(0.5)DPA_(0.5))_(x)(C6BP₀₅DPA_(0.5))_(y)        where y is a value between 0.05 and 0.5 and x=1−y. DPA is        diphenic acid represented by the following formula:

The polymer may be formed by conventional methods used to form otherpolymers containing mesogens. Consequently, the mesogen-containingpolymers may be formed by polymerizing monomers that have mesogensattached, or the polymers may be formed by polymerizing monomers havingreactive side-chains and reacting mesogen-containing compounds with thereactive side-chains.

Preferably, the polymers used to make waveplates of the inventionrequire no further reaction to complete the polymers during or afterdrawing. Certain polymers as disclosed in examples of the '514 patentdiscussed above must be drawn starting as poly(amic acid) films andimidized after or during the drawing process. The '514 patent teachesthat “performing the drawing for a polyimide film which is alreadyimidized and has no in-plane birefringence is ineffective since theconsequent in-plane birefringence is small. . . .” It is believed thatreacting the polymer (in this case imidizing) during or after drawingdecreases the repeatability of the final birefringence. The need forpolymer reaction also can increase the number of steps in themanufacturing process, increasing cost and reducing yields. In addition,in the case of polyimides, imidization performed while the film is undertensile stress may proceed incompletely, leading to an increasedsensitivity of the film to water. In the present invention, certainexamples are disclosed of performing drawing of a polymer film which isalready imidized and has no in-plane birefringence, with such drawingresulting in a high birefringence suitable for use as waveplates.

Preferably, the polymers used to make waveplates of the invention can bedrawn without appreciable solvent in the film. Certain polymers asdisclosed in examples of the '514 patent discussed above are drawn witha certain amount of solvent in the poly(amic acid) film, presumably toplasticize the film and allow the rigid poly(amic acid) film to be morereadily drawn. In practice it is difficult to control the exact amountof solvent in a film, and thus it is believed that this decreases therepeatability of achieving the desired birefringence from such a film.

Often polymers having mesogen-containing sidechains are not constrainedto be stretched in a partially-reacted state or with solvent in the filmbecause they can be easily drawn in their fully-reacted form attemperatures well below 300° C. to achieve the high degree ofbirefringence necessary for waveplates. The mesogens increase thedrawability of the polymer, allowing the fully-reacted polymer to beheated and drawn in a single step to create sufficient birefringencewith a very high degree of repeatability and uniformity.

Waveplate manufacturing processes that involve self-shrinking films, orinvolve drawing films with appreciable solvent content, or involvereactions such as imidizing after stretching may have more variabilityand may be hard to control. Such films may require in-situ monitoring ofbirefringence during the drawing process, or additional processes tofine-tune the birefringence after the drawing process. Preferably,waveplates of the invention can be drawn to a desired birefringencevalue at reasonable temperatures below 300° C. without need forsubsequent fine-tuning, and without the need for in-situ monitoring ofthe drawing or fine-tuning processes.

A waveplate formed using a polymer as described above may be moreresistant to heat and to humidity. The polymer may contain few groupsthat react with or associate with water, even under elevatedtemperatures. Further, the lower processing temperature (i.e. below 300C) made possible by certain polymers of the invention helps to preventwater vapor from reacting with or associating with components of thepolymer, thus helping to assure resistance to heat and humidity.

A waveplate for a PLC is formed by making a thin polymer film ofsuitable thickness that the finished waveplate may fit into a thincavity (about 30 μm thick or less), cut or etched into the PLC, thelength of the cavity bridging a waveguide or waveguides of interest on aPLC and the width or height of the cavity (i.e. distance into theinterior of the PLC from the outer surface of the PLC that is parallelto the waveguides of the PLC) being sufficient to cut across the heightof the waveguides of interest. The thin polymer film is thus typicallyless than 30 μm thick. Although the cavity in the PLC is typically50-300 μm in height, the waveplate is typically 1-3 mm tall for ease ofhandling during insertion into the cavity.

The film is preferably formed from a liquid solution of the polymer insolvent by methods of solvent casting known in the art (using wirewoundrod, doctor blade, Bird applicator, or spin coating, for instance) ontoa suitable substrate such as a silicon wafer or glass plate. The film ispreferably made quite large for ease of handling and increaseduniformity, formed on a substrate typically 6-12 inches in diameter fora round substrate, or 6-12 inches per side for a rectangular substrate.The film is properly dried to substantially remove the solvent, (e.g. byheating) and peeled from the substrate. A release agent may be used onthe substrate to allow the film to be easily separated from thesubstrate. A solvent or water may be used to aid in separating the filmfrom the substrate. Alternatively, the film can be made directly frompolymer without a substrate using methods such as blow-forming orextrusion.

The film is then cut to an appropriate size for a stretching apparatus.It is heated to a desired temperature, typically within 20° C. of theglass transition temperature, and stretched uniaxially or biaxiallyusing conventional techniques to obtain a thin polymer film of thedesired thickness and birefringence. It is simplest, and thuspreferable, that the film thickness is chosen such that the film can bestretched uniaxially to achieve the desired birefringence and thickness.Alternatively a thicker film can be made and stretched biaxially (withdifferent amounts of stretch along each of the two axes) to achieve thedesired birefringence and thickness. It is postulated that the polymerchains generally align along the axis of the direction of greateststretch (the “x” direction in the plane of the film, with the “y”direction being in the plane of the film and orthogonal to the “x”direction and the “z” direction being orthogonal to both the “x” and “y”directions). This generally provides a film in which the refractiveindex in the “x” direction is greater than the refractive index in the“y” direction, both of which are generally different from the refractiveindex in the “z” direction. Thus, light traveling generally along the“z” axis encounters birefringence caused primarily by the differentrefractive indices in the “x” and “y” axes.

The waveplate of the invention is typically biaxially birefringent. Suchwaveplates, as described above, exhibit a difference in refractive indexalong each of the x, y, and z axes of the film. By contrast, films ofpolymers as produced for liquid crystal display compensation layers aretypically uniaxially birefringent because these films have a constantrefractive index along two of the axes (typically the x and y axes inthe plane of the film), and a differing refractive index along the thirdaxis (typically the z axis perpendicular to the plane of the film, alongwhich light is transmitted).

Alternatively, the polymer can be solvent-cast onto a continuoussubstrate consisting of another polymer (such as polycarbonate) or ametal belt, using a continuous-roll solvent-casting and dryingapparatus. In such a system it is possible to delaminate the polymer webfrom the substrate and uniaxially stretch the polymer web in the sameapparatus. In this way a continuous roll of polymer of the desiredbirefringence and thickness can be formed.

After the polymer film is stretched, it is typically less than 30 μmthick, more typically 10-15 μm thick, with birefringence necessary toachieve quarter waveplate or half waveplate function at the desiredoperating wavelength.

After the thin polymer film is stretched to the desired birefringenceand thickness, it is then cut using a blade or shear, stamp or punch,laser, or another conventional technique to form the waveplate. Thewaveplate is cut from the film at an angle appropriate for the desireduse of the waveplate. For the typical uses of rotating TE to TM and TMto TE polarizations in a PLC using a half waveplate, or changing linearpolarizations to circular polarizations and circular polarizations tolinear polarizations in a PLC using a quarter waveplate, this angle is45° from the “x” axis, or stretch axis, of the film. While the inventionis not limited to the following dimensions, a waveplate suitable for aPLC having an arrayed waveguide grating typically has a thickness ofabout 15 μm, a height of about 2 mm, and a length of about 8 mm. Thelength of a waveplate suitable for use in a PLC typically is between 1mm and 15 mm, more typically between 5 mm and 10 mm, the height istypically between 1 mm and 3 mm, and the thickness is as discussedpreviously.

Preferably, the waveplate of the invention is capable of largepolarization conversion ratios. That is, if linearly-polarized lightincident upon a waveplate with its fast axis oriented at 45 degrees tothe polarization of the incoming light, and an analyzer is used todetect the optical energy polarized perpendicular to and parallel to thepolarization direction of the incident beam, the ratio of these opticalenergies is large. Preferably this ratio is greater than 25 dB, morepreferably greater than 30 dB.

EXAMPLES OF PLCs

The waveplate is inserted into the optical path of a waveguide. In someinstances, a small channel is etched or cut or “diced” into one or morewaveguides of the PLC, and a transmissive waveplate is inserted into thechannel. In other instances, a reflective waveguide is attached to theside of a substrate in the optical path of one or more waveguides toform a reflective waveplate.

FIG. 8 illustrates an arrayed waveguide grating (AWG) 600 as an exampleof a PLC into which a waveplate of the invention may be inserted. AWG600, which is configured as a demultiplexer, has an input waveguide 610,a first lens or expansion region 620, an array of unequal lengthwaveguides 630, a second lens 640, and multiple output waveguides 650that each receive an individual wavelength of light diffracted to itfrom the waveguides of the array through the second lens. Channel 660cut into the surface of the SiO₂ waveguides and cladding containstransmissive waveplate 670 made of a waveplate polymer as describedherein. The waveplate is generally positioned at or near the center ofthe waveguide array so that it compensates for the birefringence of thewaveguides of the array.

A wavelength multiplexer based on a Mach-Zehnder interferometer (MZI) isanother PLC into which a waveplate of the invention may be inserted.FIG. 9 illustrates first 710 and second 720 input waveguides, first 730and second 740 50% couplers, first 750 and second 760 Mach-Zehnder armwaveguides, and first 770 and second 780 output waveguides. A waveplateof the invention 790 is inserted into the waveguides of the MZI asillustrated to compensate for birefringence in the SiO₂ waveguides ofthe MZI. A waveplate of the invention may be used to form any of theoptical devices illustrated in U.S. Pat. No. 6,115,514, the disclosureof which is incorporated by reference in its entirety herein.

EXAMPLES OF WAVEPLATES Example 1

A first waveplate polymer is formulated using 4 parts PFMB, 1 part C6BP,and 5 parts bis-ADA in m-cresol to yield a random polymer having thegeneral formula shown in FIG. 6. The copolymer is formed using thefollowing formulation.

PFMB (15.18 g, 47.41 mmol), C6BP (9.21 g, 11.86 mmol) and m-cresol (345g) were added to a 500 ml three-necked round bottom flask equipped witha mechanical stirrer, a nitrogen inlet, and a distillation head. Afterthe diamine monomers dissolved in m-cresol,4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (bis-ADA)(30.24 g, 58.10 mmol) was added and the mixture was stirred at roomtemperature for one day. Isoquinoline (0.5 ml) was added and thereaction temperature was raised to 202° C. for 15 hours. After thesolution was allowed to cool to room temperature, it was slowly added tomethanol to precipitate the polymer. The polymer was dissolved inchloroform and re-precipitated in methanol and dried in vacuum oven.

This waveplate polymer is formed into a film by dissolving the polymerin a solvent such as cyclopentanone at 10-15% concentration, filteringthe solution, and casting a sheet of approximately 20-40 micronthickness using rod coating (Mayer) or Bird coating and drying thecoating in an oven or on a hotplate. The glass-transition temperature ofthe film is measured to be Tg=155° C. The resultant sheet is heated tonear or over its glass transition temperature and stretched uniaxiallyat this temperature and at a rate of about 0.25 mm per second to form afilm. The film is cooled and tested, and waveplates are cut from thecooled film at a 45 degree angle to the stretch direction.

FIG. 1 illustrates the birefringence of this film as measured in the xand y directions as a function of the amount that a small section at thecenter of the film has been stretched over its original size in the xdirection (“local elongation” (%)). The birefringence increasesmonotonically with amount of stretch, and the amount of increase issufficiently high to make a 15 μm thick half waveplate at 1550 nmwavelength. From this information, on can calculate the desired localelongation for any desired waveplate thickness. FIG. 2 shows thecalculated thickness of a half waveplate at 1550 nm wavelength and aquarter waveplate at 1550 nm wavelength as a function of the localelongation. Thus a half waveplate for 1550 nm wavelength can be createdwith thickness ranging from above 30 μm to below 10 μm.

Example 2

A polymer film is formed, and heated and stretched according toExample 1. After the film is stretched it is annealed in an oven at 145°C. for two hours. The thickness of the pre-stretched film and the degreeof elongation during the stretch are chosen such that after the film isstretched and annealed, the thickness of the film is approximately 15.6μm, and the retardance is one half wave at a wavelength of about 1550nm. A waveplate is cut from the film at a 45 degree angle to the stretchdirection. The waveplate is tested by illuminating it with polarizedlight at approximately 1550 nm wavelength polarized along the directionof the cut of the waveplate (and thus at about a 45 degree angle to thestretch axis of the waveplate). The light that is transmitted throughthe waveplate is passed through a polarizer used as an analyzer. Theoptical power transmitted through the analyzer is measured with theanalyzer perpendicular to the polarization of the input laser light, andagain with the analyzer parallel to the polarization of the input light.The ratio of these two measurements is found to be 31.9 dB. Thisdemonstrates that this film functions as a half waveplate and makes apolarization rotator with high extinction ratio.

Example 3

Two waveplates according to Example 2 are formed, one with retardance0.47 waves and one with retardance 0.67 waves at about 1550 nmwavelength. The waveplates are tested for birefringence and then bakedon a hotplate at 125° C. for 2 hours, retested, and then baked severalmore times, being retested after 8, 24, 48, 96, 192, and 288 hours onthe hotplate at 125° C. During this test, no measurable changes aredetected in waveplate retardance, demonstrating that the waveplates arethermally stable up to 125° C.

Example 4

Twelve waveplates are formed according to Example 2 each withbirefringence of about 0.5 waves at about 1550 nm wavelength andmeasured for retardance. The first four waveplates are exposed to 85° C.at 85% relative humidity (RH) for 500 hours, being measured after 24,120, and 500 hours. No measurable changes in retardance are detected,indicating that the waveplates are stable under high heat and humidity.The second four waveplates are exposed to 122° C., 98% RH, and 2atmospheres of pressure for 24 hours, being measured after 8 and 24hours. No measurable changes in retardance are detected, indicating thatthe waveplates are stable under very high heat, humidity, and pressure.The last four waveplates are exposed to thermal shock, being alternatelyexposed to 0° C. and 100° C. temperatures for 15 cycles. The waveplatesare measured after the 15 cycles, and no measurable changes inretardance are detected, indicating that the waveplates are stable underthermal shock.

Example 5

Eight arrayed-waveguide grating (AWG) chips are prepared usingsilica-on-silicon PLC technology. They are then tested for allperformance parameters typically associated with AWG devices, includinginsertion loss (IL), polarization dependent loss (PDL), uniformity,ripple, adjacent isolation, non-adjacent isolation, total isolation, andpolarization-dependent center-wavelength shift (PDW). Grooves about 20μm wide are cut into the chips in the center of the AWG grating using adicing saw. Eight half waveplates at 1550 nm wavelength about 15 μmthick are formed according to Example 2 and glued into the diced groovesof the AWG chips. All chips are then retested for the same performanceparameters and it is found that the waveplates significantly improve PDLand PDW, thus showing that the waveplates compensate for birefringencein the PLC AWG. The first four chips are then exposed to 122° C., 98%RH, and 2 atmospheres of pressure for 68 hours, being remeasured for thesame performance parameters after 8 and 68 hours. No measurable changesattributed to the waveplate are detected, indicating that the waveplatesof this invention, when inserted into AWG chips, are stable under veryhigh heat, humidity, and pressure. The second four chips are exposed tothermal shock, being alternately exposed to 0° C. and 100° C.temperatures for 100 cycles. The chips are remeasured for the sameperformance parameters after the 100 cycles, and no measurable changesare detected, indicating that the waveplates of this invention, wheninserted into AWG chips, are stable under thermal shock. The same secondfour chips are then exposed to 85° C. at 85% RH for 500 hours, beingremeasured for the same performance parameters after 214 and after 500hours. No measurable changes are detected, indicating that thewaveplates of this invention, when inserted into AWG chips, are stableunder high heat and humidity.

Example 6

Nine pre-tested arrayed-waveguide grating (AWG) chips, each with a halfwaveplate of this invention glued into the chip according to Example 5,are prepared. Optical fiber ribbons are attached to the chips and thechips are fully packaged, including temperature stabilization, usingprocesses well-known in the PLC industry. These packaged AWG devices arethen tested for all performance parameters typically associated with AWGdevices as in Example 4. Once again it is found that the waveplatescompensate for birefringence in the AWG devices. The first four packagedAWGs are then exposed to 85° C. at 85% RH for 500 hours and areremeasured for the same performance parameters. No measurable changesare detected, indicating that the waveplates of this invention, wheninserted into AWG chips and packaged, are stable under high heat andhumidity. The second four packaged AWGs are exposed to thermal cycles,each cycle consisting of successive exposure to −40° C., 21° C., 75° C.,and 21° C. for 1 hour at each temperature, with a temperature rise andfall time of 0.95° C. per minute, repeating for 63 cycles. The packagedAWG's are remeasured for the same performance parameters after 42 and 63cycles. No measurable changes are detected, indicating that thewaveplates of this invention, when inserted into AWG chips and packaged,are stable under thermal cycling. The ninth packaged AWG is exposed tohigh laser power, by launching 2 watts of optical power at approximately1480 nm wavelength into the input optical fiber of the AWG for a periodof one week. The package AWG is then remeasured for the same performanceparameters, and no measurable changes are detected, indicating that thewaveplates of this invention, when inserted into AWG chips and packaged,are stable under high laser power.

Example 7

A second waveplate polymer is formulated using 5 parts IPC, 4 partsPFMB, and 1 part C6BP, reacted in N-methylpyrrolidone (NMP) to form apolyamide random copolymer. The polymer is formed into a film using amethod similar to the polymer Example 1. The glass-transitiontemperature is measured to be Tg=216° C. The resultant sheet is heatedto near or over its glass transition temperature and stretcheduniaxially at this temperature and at a rate of about 0.25 mm per secondto form a film. The film is cooled and tested, and waveplates are cutfrom the cooled film at a 45 degree angle to the stretch direction.

FIG. 3 illustrates the birefringence of this film as measured in the xand y directions as a function of the amount that a small section at thecenter of the film has been stretched over its original size in the xdirection (“local elongation” (%)). The birefringence increasesmonotonically with amount of stretch, and the amount of increase issufficiently high to make a 15 μm thick half waveplate at 1550 nmwavelength. From this information, on can calculate the desired localelongation for any desired waveplate thickness. FIG. 4 shows thecalculated thickness of a half waveplate at 1550 nm wavelength and aquarter waveplate at 1550 nm wavelength as a function of the localelongation. Thus a half waveplate for 1550 nm wavelength can be createdwith thickness ranging from above 30 μm to below 12 μm.

Example 8

A polymer film is formed, and heated and stretched according to Example7. After the film is stretched it is annealed in an oven at 145° C. for3.5 hours. The thickness of the pre-stretched film and the degree ofelongation during the stretch are chosen such that after the film isstretched and annealed, the thickness of the film is approximately 16.3μm, and the retardance is one half wave at a wavelength of about 1550nm. A waveplate is cut from the film at a 45 degree angle to the stretchdirection. The waveplate is tested by illuminating it with polarizedlight at approximately 1550 nm wavelength polarized along the directionof the cut of the waveplate (and thus at about a 45 degree angle to thestretch axis of the waveplate). The light that is transmitted throughthe waveplate is passed through a polarizer used as an analyzer. Theoptical power transmitted through the analyzer is measured with theanalyzer perpendicular to the polarization of the input laser light, andagain with the analyzer parallel to the polarization of the input light.The ratio of these two measurements is found to be greater than 28 dB.This demonstrates that this film functions as a half waveplate and makesa polarization rotator with high extinction ratio.

Example 9

A third waveplate polymer is formulated using 1 part bis-ADA and 1 partC6BP using processing analogous to that of Example 1. The waveplatepolymer is dissolved in NMP at 3-5% concentration and made into a thinfilm by depositing the polymer solution on a glass substrate and bakingout the solvent on a covered hotplate. The film is drawn uniaxially at90 C to three times its starting length (i.e. draw ratio of 200%), andthe stretched film having a thickness of 14 micron is almosttransparent. The refractive indices in the plane of the film paralleland perpendicular to the stretch direction are measured in a prismcoupler manufactured by Metricon at wavelength 633 nm. In the stretchdirection the refractive index is measured twice, giving values of1.7116 and 1.7122. In the direction perpendicular to the stretchdirection the refractive index is again measured twice, giving values of1.6135 and 1.6137. From this the birefringence wavelength is calculatedto be 0.098, indicating that the polymer has achieved highbirefringence. The birefringence of the film at 1550 nm is estimated tobe 0.094. Thus with this amount of stretch, this polymer is suitable fora half waveplate at 1550 nm with 8.3 μm thickness.

Example 10

A polymer waveplate is formed using the polymer and procedure of Example9, but the waveplate polymer is drawn uniaxially at 100° C. to twice itsstarting length (i.e. draw ratio of 100%), and the stretched film havinga thickness of 9.5-10 microns is transparent and colorless. Therefractive indices in the plane of the film parallel and perpendicularto the stretch direction are measured in a prism coupler manufactured byMetricon at wavelength 633 nm. In the stretch direction the refractiveindex is measured twice, giving values of 1.6941 and 1.6941. In thedirection perpendicular to the stretch direction the refractive index isagain measured twice, giving values of 1.6128 and 1.6128. From this thebirefringence at 633 nm wavelength is calculated to be 0.081. Theretardance of the film is subsequently measured at wavelength of about1550 nm to be 0.45 waves. The birefringence at 1550 nm is thuscalculated to be 0.070. Thus with this amount of stretch, this polymeris suitable for a half waveplate at 1550 nm with 11.1 μm thickness.

Example 11

A polymer waveplate is formed using the polymer and procedure of Example10, but the waveplate polymer is drawn to a draw ratio of 80%. Thethickness of the film prior to stretching is 16 micron, and thethickness after stretching is 10 micron. The film is transparent andcolorless. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured twice, giving values of 1.6910 and1.6908. In the direction perpendicular to the stretch direction therefractive index is again measured twice, giving values of 1.6152 and1.6152. From this the birefringence at 633 nm is calculated to be 0.076,indicating that the polymer has achieved high birefringence. Theretardance of the film is subsequently measured at wavelength of about1550 nm to be 0.36 waves. The birefringence at 1550 nm is thuscalculated to be 0.056. Thus with this amount of stretch, this polymeris suitable for a half waveplate at 1550 nm with 13.9 μm thickness.

Example 12

A fourth waveplate polymer is formulated of 4 parts 6FDA, 3 parts PFMB,and 1 part C6BP, and the waveplate polymer is drawn uniaxially in the xdirection at 200 C to a draw ratio of 100% and a thickness of 12 micron.The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured twice, giving values of 1.6111 and1.6112. In the direction perpendicular to the stretch direction therefractive index is again measured twice, giving values of 1.5567 and1.5569. From this the birefringence at 633 nm is calculated to be 0.054,indicating that the polymer has achieved high birefringence. Thebirefringence of the film at 1550 nm is estimated to be 0.052. Thus withthis amount of stretch, this polymer is suitable for a half waveplate at1550 nm with 15 μm thickness.

Example 13

A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and 1 partC6BP, and the waveplate polymer is drawn uniaxially in the x directionat 210 C to a draw ratio of 100% and a thickness of 12 micron. Therefractive indices in the plane of the film parallel and perpendicularto the stretch direction are measured in a prism coupler manufactured byMetricon at wavelength 633 nm. In the stretch direction the refractiveindex is measured twice, giving values of 1.6215 and 1.6222. In thedirection perpendicular to the stretch direction the refractive index isagain measured twice, giving values of 1.5540 and 1.5560. From this thebirefringence at 633 nm is calculated to be 0.067, indicating that thepolymer has achieved high birefringence. The birefringence of the filmat 1550 nm is estimated to be 0.064. Thus with this amount of stretch,this polymer is suitable for a half waveplate at 1550 nm with 12.2 μmthickness.

Example 14

A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and 1 partC6BP, and the waveplate polymer is drawn uniaxially in the x directionat 215 C to a draw ratio of 100% and a thickness of 13 micron. Therefractive indices in the plane of the film parallel and perpendicularto the stretch direction are measured in a prism coupler manufactured byMetricon at wavelength 633 nm. In the stretch direction the refractiveindex is measured twice, giving values of 1.6156 and 1.6152. In thedirection perpendicular to the stretch direction the refractive index isagain measured twice, giving values of 1.5571 and 1.5571. From this thebirefringence at 633 nm is calculated to be 0.058, indicating that thepolymer has achieved high birefringence. The birefringence of the filmat 1550 nm is estimated to be 0.055. Thus with this amount of stretch,this polymer is suitable for a half waveplate at 1550 nm with 14 μmthickness.

Example 15

A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and 1 partC6BP, and the waveplate polymer is drawn uniaxially in the x directionat 220 C to a draw ratio of 80% and a thickness of 12.5 micron. Therefractive indices in the plane of the film parallel and perpendicularto the stretch direction are measured in a prism coupler manufactured byMetricon at wavelength 633 nm. In the stretch direction the refractiveindex is measured twice, giving values of 1.6159 and 1.6158. In thedirection perpendicular to the stretch direction the refractive index isagain measured twice, giving values of 1.5542 and 1.5545. From this thebirefringence at 633 nm is calculated to be 0.062, indicating that thepolymer has achieved high birefringence. The birefringence of the filmat 1550 nm is estimated to be 0.058. Thus with this amount of stretch,this polymer is suitable for a half waveplate at 1550 nm with 13.2 μmthickness.

Example 16

A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and 1 partC6BP, and the waveplate polymer is drawn uniaxially in the x directionat 230 C to a draw ratio of 93.75% and a thickness of 14 micron. Therefractive indices in the plane of the film parallel and perpendicularto the stretch direction are measured in a prism coupler manufactured byMetricon at wavelength 633 nm. In the stretch direction the refractiveindex is measured multiple times, giving average value 1.6098. In thedirection perpendicular to the stretch direction the refractive index isagain measured, giving average value 1.5622. From this the birefringenceat 633 nm is calculated to be 0.048, indicating that the polymer hasachieved high birefringence. The retardance of the film is subsequentlymeasured at wavelength of about 1550 nm to be 0.38 waves. Thebirefringence at 1550 nm is thus calculated to be 0.042. Thus with thisamount of stretch, this polymer is suitable for a half waveplate at 1550nm with 18.3 μm thickness.

Example 17

A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and 1 partC6BP, and the waveplate polymer is drawn uniaxially in the x directionat 230 C to a draw ratio of 110% and a thickness of 14 micron. Therefractive indices in the plane of the film parallel and perpendicularto the stretch direction are measured in a prism coupler manufactured byMetricon at wavelength 633 nm. In the stretch direction the refractiveindex is measured multiple times, giving average value 1.6207. In thedirection perpendicular to the stretch direction the refractive index isagain measured, giving average value 1.5600. From this the birefringenceat 633 nm is calculated to be 0.061, indicating that the polymer hasachieved high birefringence. The retardance of the film is subsequentlymeasured at wavelength of about 1550 nm to be 0.53 waves. Thebirefringence at 1550 nm is thus calculated to be 0.059. Thus with thisamount of stretch, this polymer is suitable for a half waveplate at 1550nm with 13.2 μm thickness.

Example 18

A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and 1 partC6BP, and the waveplate polymer is drawn uniaxially in the x directionat 240 C to a draw ratio of 107% and a thickness of 13.5 micron. Therefractive indices in the plane of the film parallel and perpendicularto the stretch direction are measured in a prism coupler manufactured byMetricon at wavelength 633 nm. In the stretch direction the refractiveindex is measured multiple times, giving average value 1.6181. In thedirection perpendicular to the stretch direction the refractive index isagain measured, giving average value 1.5602. From this the birefringenceat 633 nm is calculated to be 0.058, indicating that the polymer hasachieved high birefringence. The retardance of the film is subsequentlymeasured at wavelength of about 1550 nm to be 0.47 waves. Thebirefringence at 1550 nm is thus calculated to be 0.054. Thus with thisamount of stretch, this polymer is suitable for a half waveplate at 1550nm with 14.2 μm thickness.

Example 19

A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and 1 partC6BP, and the waveplate polymer is drawn uniaxially in the x directionat 230 C to a draw ratio of 100% and a thickness of 16.5 micron. Therefractive indices in the plane of the film parallel and perpendicularto the stretch direction are measured in a prism coupler manufactured byMetricon at wavelength 633 nm. In the stretch direction the refractiveindex is measured multiple times, giving average value 1.6104. In thedirection perpendicular to the stretch direction the refractive index isagain measured, giving average value 1.5642. From this the birefringenceat 633 nm is calculated to be 0.046, indicating that the polymer hasachieved high birefringence. The retardance of the film is subsequentlymeasured at wavelength of about 1550 nm to be 0.41 waves. Thebirefringence at 1550 nm is thus calculated to be 0.047. Thus with thisamount of stretch, this polymer is suitable for a half waveplate at 1550nm with 16.3 μm thickness.

Example 20

A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and 1 partC6BP, and the waveplate polymer is drawn uniaxially in the x directionat 230 C to a draw ratio of 107% and a thickness of 14 micron. Therefractive indices in the plane of the film parallel and perpendicularto the stretch direction are measured in a prism coupler manufactured byMetricon at wavelength 633 nm. In the stretch direction the refractiveindex is measured multiple times, giving average value 1.6153. In thedirection perpendicular to the stretch direction the refractive index isagain measured, giving average value 1.5579. From this the birefringenceat 633 nm is calculated to be 0.057, indicating that the polymer hasachieved high birefringence. The retardance of the film is subsequentlymeasured at wavelength of about 1550 nm to be 0.47 waves. Thebirefringence at 1550 nm is thus calculated to be 0.054. Thus with thisamount of stretch, this polymer is suitable for a half waveplate at 1550nm with 14.4 μm thickness.

Example 21

A fifth waveplate polymer is formulated 9 parts bis-ADA, 1 part 6FDA, 8parts PFMB, and 2 parts C6BP, and the waveplate polymer is drawnuniaxially in the x direction at 190 C to a draw ratio of 50% and athickness of 12 micron. The retardance of the film is subsequentlymeasured at wavelength of about 1550 nm to be 0.5 waves. Thebirefringence at 1550 nm is thus calculated to be 0.065.

Example 22 Preparation of PFMB (FIG. 10) 2-Iodotrifluoromethylbenzene(1)

A 4-L beaker, equipped with a mechanical stirrer, a thermometer and anaddition funnel was charged with 560 ml of concentrated hydrochloricacid and 640 g of ice. After the mixture was stirred and cooled to 0°C., 250 ml of 2-trifluoromethylaniline (2.00 mol) was added slowly.After the addition was complete, the mixture was stirred for 10 minutes,and 141.0 g of sodium nitrite in 400 ml of cold water was adder dropwiseso as to maintain the temperature below 0° C. The reaction mixture wasstirred at 0° C. for an additional 30 minutes and then filtered. Thefiltrate, which was maintained at 0° C., was added dropwise to a 4-Lbeaker charged with 381.2 g of potassium iodide in 1000 ml of watercooled to 0° C. After the addition, the reaction mixture was stirred foran additional 30 minutes at 0° C. and then for one hour at roomtemperature. The mixture was placed in a separatory funnel, and theorganic layer was separated. The water layer was extracted withmethylene chloride. The organic phase was washed with an aqueous sodiumbisulfite solution several times and then dried over anhydrous magnesiumsulfate. The solution was filtered and the methylene chloride wasremoved under reduced pressure to afford 510.9 g (94%) of a pale orangeoil.

2,2′-Bis(trifluoromethyl)biphenyl (2)

To a 2-L three-necked, round-bottom flask fitted with a mechanicalstirrer and a condenser was added 507.5 g of2-iodotrifluoromethylbenzene (1.86 mol), 282.0 g of copper powder and400 ml of DMF. The reaction mixture was stirred and heated at reflux for24 hours and filtered. The filtrate was distilled under reduced pressureto yield 211.8 g (78%) of a light yellow oil.

2,2′-Bis(trifluoromethyl)-4,4′-dinitrobiphenyl (3)

To a 2-L three-necked, round-bottom flask equipped with a mechanicalstirrer, a thermometer and an addition funnel was added 210.0 g of2,2′-bis(trifluoromethyl)biphenyl and 725.0 g of concentrated sulfuricacid. After the stirred mixture was cooled to room temperature, 140.0 gof 70% concentrated nitric acid was added dropwise. After the additionwas complete, the reaction mixture was heated slowly to 140° C., andanother 67 g of 70% concentrated nitric acid was added. The reactionmixture was stirred at room temperature overnight and poured into icewater. The solid that precipitated was collected by filtration andwashed with water. The solid was recrystallized from acetone/ethanol toafford 199.1 g (72%) of light yellow crystals.

2,2′-Bis-(trifluoromethyl)4,4′-diaminobiphenyl (4, PFMB)

A hydrogenation bottle was charged with 40.0 g of2,2′-bis(trifluoromethyl)-4,4′-dinitrobiphenyl, 0.6 g of 5% palladium onactivated carbon and 200 ml of ethyl acetate. The bottle was secured ona Parr hydrogenation apparatus, flushed five times with hydrogen, andthen pressurized with hydrogen to 56 psi. The pressure was maintained,and the vessel was agitated for several hours. After the reactionmixture was filtered and about 200 ml of hexanes were added. Thecrystals that formed were filtered to afford 30.2 g (90%) of product.

Preparation of C6BP (FIG. 11) 6-Bromo-1-hexanol (5)

A mixture of 1,6-hexanediol (454.4 g, 3.84 mol), hydrobromic acid (48%wt, 651.3 g, 3.86 mol), and concentrated sulfuric acid (220.0 g) wasstirred at room temperature for two days and then heated at reflux for 3hours. After the solution was allowed to cool to room temperature, thesolution was extracted with methylene chloride three times. The extractwas washed with water several times and dried over magnesium sulfate.The ethyl ether was removed on a rotary evaporator to give a brownliquid, which was chromatographed on a silica gel column with hexane asthe eluent, and then with a mixture of ethyl acetate and hexane (1:1) asthe eluent. The product fraction was collected and the solvents wereremoved under reduced pressure to afford 291.3 g (42%) of a light yellowclear liquid: ¹H-NMR (CDCl3) δ (ppm): 1.31-1.97 (m, 8H), 3.38 (t, 2H),3.61 (t, 2H).

4-(6-Hydroxyhexoxy)biphenyl (6)

To a 4 L three-necked round bottom flask fitted with a mechanicalstirrer and a condenser were added 125.0 g of 4-hydroxybiphenyl (0.734mol), 154.5 g of 6-bromo-1-hexanol (0.853 mol), 690 g of potassiumcarbonate, and 2500 ml of acetone. The reaction mixture was stirred andheated at reflux for 4 days and then filtered. The acetone was removedon a rotary evaporator, the residue was recrystallized from a mixture ofethyl acetate and hexanes to afford 188 g of white crystals (95%): mp92-94° C.; 1H-NMR (CDCl₃) δ (ppm) 1.30-1.84 (m, 8H), 3.65 (t, 2H), 3.99(t, 2H), 6.98 (d, 2H), 7.32-7.56 (m, 7H).

4,4′-Dinitrodiphenic Acid (7)

To a 1000 ml, three-necked, round-bottom flask equipped with amechanical stirrer, a thermometer and an addition funnel were added 30.0g of diphenic acid (2,2′-diphenyldicarboxylic acid) (0.123 mol) and 469g of concentrated sulfuric acid. After the diphenic acid dissolved toform a yellow solution, the mixture was cooled to −15° C. in a dry icebath. In a separate Erlenmeyer flask, concentrated nitric acid (70% wt,92.4 g, 1.03 mol) and concentrated sulfuric acid (12.0 g) were mixed andtransferred to the addition funnel. The acid mixture was added slowly tothe diphenic acid solution so that the mixture was maintained below 0°C. After the addition was complete, the reaction mixture was allowed towarm to room temperature and stirred for 24 hours. After the mixture waspoured onto crushed ice, the precipitate that formed was collected byfiltration and washed with water. The solid was dissolved in a 10%aqueous solution of sodium hydroxide, and the insoluble portion wasremoved by filtration. The filtrate was acidified with concentratedhydrochloric acid. The precipitate was collected and recrystallizedfirst from a mixture of ethanol and water twice to give 36.5 g of lightyellow crystals (89.5%); mp 255-258° C. (lit. mp 258-259° C.); 1H-NMR(DMSO-d6) δ (ppm) 7.53 (d, 2H), 8.44 (dd, 2H,) and 8.67 (d, 2H).

Bis{6-[4-biphenyloxy]hexyl}4,4′-dinitro-2,2′-biphenyldicarboxylate (8)

To a 500 ml Erlenmeyer flask fitted with a magnetic stirring bar wereadded 9.8 g of 4,4′-dinitrodiphenic acid (2) (29.6 mmol), 17.0 g of6-hydroxyhexoxybiphenyl (6) (62.8 mmol), 13.2 g ofdicyclohexylcarbodiimide (64.2 mmol), 0.5 g of dimethylaminopyridine,and 400 ml of methylene chloride. The mixture was stirred at roomtemperature overnight and filtered. The filtrate was taken to dryness ona rotary evaporator to give an orange solid. The solid wasrecrystallized from ethyl acetate/hexanes to afford 16.5 g (67%) oflight yellow crystals, mp: 121-122° C. ¹H-NMR (d-CDCl₃) δ (ppm) 1.2-1.8(m, 16H), 3.9 (t, 4H), 4.1 (t, 4H), 6.9 (d, 4H), 7.2-7.6 (m, 16H), 8.4(dd, 2H) and 8.9 (d, 2H).

Bis{6-[4-biphenyloxy]hexyl}4,4′-diamino-2,2′-biphenyldicarboxylate (9,C6BP)

Bis{6-[4-biphenyloxy]hexyl}4,4′-dinitro-2,2′-biphenyldicarboxylate (8)(2.26 g, 2.70 mol), palladium on activated carbon (5%, 0.31 g), andtetrahydrofuran (50 ml) were added to a hydrogenation bottle. The bottlewas secured on a Parr hydrogenation apparatus, flushed five times withhydrogen, then pressurized with hydrogen to 56 psi. The pressure wasmaintained and the vessel was agitated for 24 hours. After the reactionmixture was filtered and about 100 ml of hexanes were added torecrystallize the products directly to afford 1.7 g (80%) of lightyellow crystals. mp: 122-124° C. ¹H-NMR (CDCl₃) δ (ppm) 1.2-1.8 (m,16H), 3.9 (m, 8H), 6.8-7.6 (m, 24H).

TABLE 1 Examples of backbones, mesogens, linkers, and optional spacers“X” GROUP “R” GROUP BACKBONE OF OF LINKER OPTIONAL SPACER DESIGNATION(“B”) MESOGEN MESOGEN (“L”) (“S”) 1 polycarbonate (none) hydrogen etherpoly(alkylene oxide) 2 polyolefin axo alkyl ester polyalkane 3polysulfone diazo cycloalkyl amide polyperfluoroalkane 4 polyphenyleneazoxy aryl imide polysiloxane 5 polyimide nitrone aralkyl urethanealiphatic polyether 6 polyamideimide carbon-carbon alkaryl alkylenedouble bond 7 polyesterimide carbon-carbon cyano alkyl triple bond 8polyetherimide amide alkoxy 9 polyketone imide acyloxy 10polyetherketone Schiff base halogen 11 polybenz- ester oxazole 12polyoxa-diazole 13 polybenzo- thiazole 14 polythia-diazole 15polyquin-oxaline 16 polybenz- imidazole 17 polyacetal 18 polysulfone 19polysulfide 20 polythioester 21 polysulfon- amide 22 polyamide 23polyurethane 24 polyurea 25 polyimine 26 poly- phosphazene 27 polysilane28 polysiloxane 29 polysilazane 30 polyether 31 polycarbonate 32polyester 33 polyphenylene 34 polydiene 35 polyalkene 36 polyacrylate 37polyvinyl ether 38 polyvinyl ketone 39 polyvinyl halide 40 polyvinylnitrile 41 polyvinyl ester 42 polystyrene 43 polyarylether 44polyarylene

TABLE 2 Polymers used to form waveplates polyimide backbone withphenyl-phenyl mesogen polyimide backbone with phenyl-phenyl-cyanomesogen polyimide backbone with phenyl-phenyl-acyloxy mesogen polyimidebackbone with phenyl-phenyl-alkyl mesogen polyimide backbone withphenyl-phenyl-aryl mesogen polyimide backbone with phenyl-C double bondC-phenyl mesogen polyimide backbone with phenyl-C double bondC-phenyl-cyano mesogen polyimide backbone with phenyl-C double bondC-phenyl-acyloxy mesogen polyimide backbone with phenyl-C double bondC-phenyl-alkyl mesogen polyimide backbone with phenyl-C double bondC-phenyl-aryl mesogen polyimide backbone with phenyl-C triple bondC-phenyl mesogen polyimide backbone with phenyl-C triple bondC-phenyl-cyano mesogen polyimide backbone with phenyl-C triple bondC-phenyl-acyloxy mesogen polyimide backbone with phenyl-C triple bondC-phenyl-alkyl mesogen polyimide backbone with phenyl-C triple bondC-phenyl-aryl mesogen polyimide backbone with phenyl-ester-phenylmesogen polyimide backbone with phenyl-ester-phenyl-cyano mesogenpolyimide backbone with phenyl-ester-phenyl-acyloxy mesogen polyimidebackbone with phenyl-ester-phenyl-alkyl mesogen polyimide backbone withphenyl-ester-phenyl-aryl mesogen polyimide backbone withphenyl-amide-phenyl mesogen polyimide backbone withphenyl-amide-phenyl-cyano mesogen polyimide backbone withphenyl-amide-phenyl-acyloxy mesogen polyimide backbone withphenyl-amide-phenyl-alkyl mesogen polyimide backbone withphenyl-amide-phenyl-aryl mesogen polyimide backbone withphenyl-azo-phenyl mesogen polyimide backbone withphenyl-azo-phenyl-cyano mesogen polyimide backbone withphenyl-azo-phenyl-acyloxy mesogen polyimide backbone withphenyl-azo-phenyl-alkyl mesogen polyimide backbone withphenyl-azo-phenyl-aryl mesogen polyetherimide backbone withphenyl-phenyl mesogen polyetherimide backbone with phenyl-phenyl-cyanomesogen polyetherimide backbone with phenyl-phenyl-acyloxy mesogenpolyetherimide backbone with phenyl-phenyl-alkyl mesogen polyetherimidebackbone with phenyl-phenyl-aryl mesogen polyetherimide backbone withphenyl-C double bond C-phenyl mesogen polyetherimide backbone withphenyl-C double bond C-phenyl-cyano mesogen polyetherimide backbone withphenyl-C double bond C-phenyl-acyloxy mesogen polyetherimide backbonewith phenyl-C double bond C-phenyl-alkyl mesogen polyetherimide backbonephenyl-C double bond C-phenyl-aryl mesogen polyetherimide backbone withphenyl-C triple bond C-phenyl mesogen polyetherimide backbone withphenyl-C triple bond C-phenyl-cyano mesogen polyetherimide backbone withphenyl-C triple bond C-phenyl-acyloxy mesogen polyetherimide backbonewith phenyl-C triple bond C-phenyl-alkyl mesogen polyetherimide backbonewith phenyl-C triple bond C-phenyl-aryl mesogen polyetherimide backbonewith phenyl-ester-phenyl mesogen polyetherimide backbone withphenyl-ester-phenyl-cyano mesogen polyetherimide backbone withphenyl-ester-phenyl-acyloxy mesogen polyetherimide backbone withphenyl-ester-phenyl-alkyl mesogen polyetherimide backbone withphenyl-ester-phenyl-aryl mesogen polyetherimide backbone withphenyl-amide-phenyl mesogen polyetherimide backbone withphenyl-amide-phenyl-cyano mesogen polyetherimide backbone withphenyl-amide-phenyl-acyloxy mesogen polyetherimide backbone withphenyl-amide-phenyl-alkyl mesogen polyetherimide backbone withphenyl-amide-phenyl-aryl mesogen polyetherimide backbone withphenyl-azo-phenyl mesogen polyetherimide backbone withphenyl-azo-phenyl-cyano mesogen polyetherimide backbone withphenyl-azo-phenyl-acyloxy mesogen polyetherimide backbone withphenyl-azo-phenyl-alkyl mesogen polyetherimide backbone withphenyl-azo-phenyl-aryl mesogen polyesterimide backbone withphenyl-phenyl mesogen polyesterimide backbone with phenyl-phenyl-cyanomesogen polyesterimide backbone with phenyl-phenyl-acyloxy mesogenpolyesterimide backbone with phenyl-phenyl-alkyl mesogen polyesterimidebackbone with phenyl-phenyl-aryl mesogen polyesterimide backbone withphenyl-C double bond C-phenyl mesogen polyesterimide backbone withphenyl-C double bond C-phenyl-cyano mesogen polyesterimide backbone withphenyl-C double bond C-phenyl-acyloxy mesogen polyesterimide backbonewith phenyl-C double bond C-phenyl-alkyl mesogen polyesterimide backbonewith phenyl-C double bond C-phenyl-aryl mesogen polyesterimide backbonewith phenyl-C triple bond C-phenyl mesogen polyesterimide backbone withphenyl-C triple bond C-phenyl-cyano mesogen polyesterimide backbone withphenyl-C triple bond C-phenyl-acyloxy mesogen polyesterimide backbonewith phenyl-C triple bond C-phenyl-alkyl mesogen polyesterimide backbonewith phenyl-C triple bond C-phenyl-aryl mesogen polyesterimide backbonewith phenyl-ester-phenyl mesogen polyesterimide backbone withphenyl-ester-phenyl-cyano mesogen polyesterimide backbone withphenyl-ester-phenyl-acyloxy mesogen polyesterimide backbone withphenyl-ester-phenyl-alkyl mesogen polyesterimide backbone withphenyl-ester-phenyl-aryl mesogen polyesterimide backbone withphenyl-amide-phenyl mesogen polyesterimide backbone withphenyl-amide-phenyl-cyano mesogen polyesterimide backbone withphenyl-amide-phenyl-acyloxy mesogen polyesterimide backbone withphenyl-amide-phenyl-alkyl mesogen polyesterimide backbone withphenyl-amide-phenyl-aryl mesogen polyesterimide backbone withphenyl-azo-phenyl mesogen polyesterimide backbone withphenyl-azo-phenyl-cyano mesogen polyesterimide backbone withphenyl-azo-phenyl-acyloxy mesogen polyesterimide backbone withphenyl-azo-phenyl-alkyl mesogen polyesterimide backbone withphenyl-azo-phenyl-aryl mesogen polyamideimide backbone withphenyl-phenyl mesogen polyamideimide backbone with phenyl-phenyl-cyanomesogen polyamideimide backbone with phenyl-phenyl-acyloxy mesogenpolyamideimide backbone with phenyl-phenyl-alkyl mesogen polyamideimidebackbone with phenyl-phenyl-aryl mesogen polyamideimide backbone withphenyl-C double bond C-phenyl mesogen polyamideimide backbone withphenyl-C double bond C-phenyl-cyano mesogen polyamideimide backbone withphenyl-C double bond C-phenyl-acyloxy mesogen polyamideimide backbonewith phenyl-C double bond C-phenyl-alkyl mesogen polyamideimide backbonewith phenyl-C double bond C-phenyl-aryl mesogen polyamideimide backbonewith phenyl-C triple bond C-phenyl mesogen polyamideimide backbone withphenyl-C triple bond C-phenyl-cyano mesogen polyamideimide backbone withphenyl-C triple bond C-phenyl-acyloxy mesogen polyamideimide backbonewith phenyl-C triple bond C-phenyl-alkyl mesogen polyamideimide backbonewith phenyl-C triple bond C-phenyl-aryl mesogen polyamideimide backbonewith phenyl-ester-phenyl mesogen polyamideimide backbone withphenyl-ester-phenyl-cyano mesogen polyamideimide backbone withphenyl-ester-phenyl-acyloxy mesogen polyamideimide backbone withphenyl-ester-phenyl-alkyl mesogen polyamideimide backbone withphenyl-ester-phenyl-aryl mesogen polyamideimide backbone withphenyl-amide-phenyl mesogen polyamideimide backbone withphenyl-amide-phenyl-cyano mesogen polyamideimide backbone withphenyl-amide-phenyl-acyloxy mesogen polyamideimide backbone withphenyl-amide-phenyl-alkyl mesogen polyamideimide backbone withphenyl-amide-phenyl-aryl mesogen polyamideimide backbone withphenyl-azo-phenyl mesogen polyamideimide backbone withphenyl-azo-phenyl-cyano mesogen polyamideimide backbone withphenyl-azo-phenyl-acyloxy mesogen polyamideimide backbone withphenyl-azo-phenyl-alkyl mesogen polyamideimide backbone withphenyl-azo-phenyl-aryl mesogen polyketone backbone with phenyl-phenylmesogen polyketone backbone with phenyl-phenyl-cyano mesogen polyketonebackbone with phenyl-phenyl-acyloxy mesogen polyketone backbone withphenyl-phenyl-alkyl mesogen polyketone backbone with phenyl-phenyl-arylmesogen polyketone backbone with phenyl-C double bond C-phenyl mesogenpolyketone backbone with phenyl-C double bond C-phenyl-cyano mesogenpolyketone backbone with phenyl-C double bond C-phenyl-acyloxy mesogenpolyketone backbone with phenyl-C double bond C-phenyl-alkyl mesogenpolyketone backbone with phenyl-C double bond C-phenyl-aryl mesogenpolyketone backbone with phenyl-C triple bond C-phenyl mesogenpolyketone backbone with phenyl-C triple bond C-phenyl-cyano mesogenpolyketone backbone with phenyl-C triple bond C-phenyl-acyloxy mesogenpolyketone backbone with phenyl-C triple bond C-phenyl-alkyl mesogenpolyketone backbone with phenyl-C triple bond C-phenyl-aryl mesogenpolyketone backbone with phenyl-ester-phenyl mesogen polyketone backbonewith phenyl-ester-phenyl-cyano mesogen polyketone backbone withphenyl-ester-phenyl-acyloxy mesogen polyketone backbone withphenyl-ester-phenyl-alkyl mesogen polyketone backbone withphenyl-ester-phenyl-aryl mesogen polyketone backbone withphenyl-amide-phenyl mesogen polyketone backbone withphenyl-amide-phenyl-cyano mesogen polyketone backbone withphenyl-amide-phenyl-acyloxy mesogen polyketone backbone withphenyl-amide-phenyl-alkyl mesogen polyketone backbone withphenyl-amide-phenyl-aryl mesogen polyketone backbone withphenyl-azo-phenyl mesogen polyketone backbone withphenyl-azo-phenyl-cyano mesogen polyketone backbone withphenyl-azo-phenyl-acyloxy mesogen polyketone backbone withphenyl-azo-phenyl-alkyl mesogen polyketone backbone withphenyl-azo-phenyl-aryl mesogen polyarylethers backbone withphenyl-phenyl mesogen polyarylethers backbone with phenyl-phenyl-cyanomesogen polyarylethers backbone with phenyl-phenyl-acyloxy mesogenpolyarylethers backbone with phenyl-phenyl-alkyl mesogen polyarylethersbackbone with phenyl-phenyl-aryl mesogen polyarylethers backbone withphenyl-C double bond C-phenyl mesogen polyarylethers backbone withphenyl-C double bond C-phenyl-cyano mesogen polyarylethers backbone withphenyl-C double bond C-phenyl-acyloxy mesogen polyarylethers backbonewith phenyl-C double bond C-phenyl-alkyl mesogen polyarylethers backbonewith phenyl-C double bond C-phenyl-aryl mesogen polyarylethers backbonewith phenyl-C triple bond C-phenyl mesogen polyarylethers backbone withphenyl-C triple bond C-phenyl-cyano mesogen polyarylethers backbone withphenyl-C triple bond C-phenyl-acyloxy mesogen polyarylethers backbonewith phenyl-C triple bond C-phenyl-alkyl mesogen polyarylethers backbonewith phenyl-C triple bond C-phenyl-aryl mesogen polyarylethers backbonewith phenyl-ester-phenyl mesogen polyarylethers backbone withphenyl-ester-phenyl-cyano mesogen polyarylethers backbone withphenyl-ester-phenyl-acyloxy mesogen polyarylethers backbone withphenyl-ester-phenyl-alkyl mesogen polyarylethers backbone withphenyl-ester-phenyl-aryl mesogen polyarylethers backbone withphenyl-amide-phenyl mesogen polyarylethers backbone withphenyl-amide-phenyl-cyano mesogen polyarylethers backbone withphenyl-amide-phenyl-acyloxy mesogen polyarylethers backbone withphenyl-amide-phenyl-alkyl mesogen polyarylethers backbone withphenyl-amide-phenyl-aryl mesogen polyarylethers backbone withphenyl-azo-phenyl mesogen polyarylethers backbone withphenyl-azo-phenyl-cyano mesogen polyarylethers backbone withphenyl-azo-phenyl-acyloxy mesogen polyarylethers backbone withphenyl-azo-phenyl-alkyl mesogen polyarylethers backbone withphenyl-azo-phenyl-aryl mesogen polyetherketone backbone withphenyl-phenyl mesogen polyetherketone backbone with phenyl-phenyl-cyanomesogen polyetherketone backbone with phenyl-phenyl-acyloxy mesogenpolyetherketone backbone with phenyl-phenyl-alkyl mesogenpolyetherketone backbone with phenyl-phenyl-aryl mesogen polyetherketonebackbone with phenyl-C double bond C-phenyl mesogen polyetherketonebackbone with phenyl-C double bond C-phenyl-cyano mesogenpolyetherketone backbone with phenyl-C double bond C-phenyl-acyloxymesogen polyetherketone backbone with phenyl-C double bondC-phenyl-alkyl mesogen polyetherketone backbone with phenyl-C doublebond C-phenyl-aryl mesogen polyetherketone backbone with phenyl-C triplebond C-phenyl mesogen polyetherketone backbone with phenyl-C triple bondC-phenyl-cyano mesogen polyetherketone backbone with phenyl-C triplebond C-phenyl-acyloxy mesogen polyetherketone backbone with phenyl-Ctriple bond C-phenyl-alkyl mesogen polyetherketone backbone withphenyl-C triple bond C-phenyl-aryl mesogen polyetherketone backbone withphenyl-ester-phenyl mesogen polyetherketone backbone withphenyl-ester-phenyl-cyano mesogen polyetherketone backbone withphenyl-ester-phenyl-acyloxy mesogen polyetherketone backbone withphenyl-ester-phenyl-alkyl mesogen polyetherketone backbone withphenyl-ester-phenyl-aryl mesogen polyetherketone backbone withphenyl-amide-phenyl mesogen polyetherketone backbone withphenyl-amide-phenyl-cyano mesogen polyetherketone backbone withphenyl-amide-phenyl-acyloxy mesogen polyetherketone backbone withphenyl-amide-phenyl-alkyl mesogen polyetherketone backbone withphenyl-amide-phenyl-aryl mesogen polyetherketone backbone withphenyl-azo-phenyl mesogen polyetherketone backbone withphenyl-azo-phenyl-cyano mesogen polyetherketone backbone withphenyl-azo-phenyl-acyloxy mesogen polyetherketone backbone withphenyl-azo-phenyl-alkyl mesogen polyetherketone backbone withphenyl-azo-phenyl-aryl mesogen polysulfone backbone with phenyl-phenylmesogen polysulfone backbone with phenyl-phenyl-cyano mesogenpolysulfone backbone with phenyl-phenyl-acyloxy mesogen polysulfonebackbone with phenyl-phenyl-alkyl mesogen polysulfone backbone withphenyl-phenyl-aryl mesogen polysulfone backbone with phenyl-C doublebond C-phenyl mesogen polysulfone backbone with phenyl-C double bondC-phenyl-cyano mesogen polysulfone backbone with phenyl-C double bondC-phenyl-acyloxy mesogen polysulfone backbone with phenyl-C double bondC-phenyl-alkyl mesogen polysulfone backbone with phenyl-C double bondC-phenyl-aryl mesogen polysulfone backbone with phenyl-C triple bondC-phenyl mesogen polysulfone backbone with phenyl-C triple bondC-phenyl-cyano mesogen polysulfone backbone with phenyl-C triple bondC-phenyl-acyloxy mesogen polysulfone backbone with phenyl-C triple bondC-phenyl-alkyl mesogen polysulfone backbone with phenyl-C triple bondC-phenyl-aryl mesogen polysulfone backbone with phenyl-ester-phenylmesogen polysulfone backbone with phenyl-ester-phenyl-cyano mesogenpolysulfone backbone with phenyl-ester-phenyl-acyloxy mesogenpolysulfone backbone with phenyl-ester-phenyl-alkyl mesogen polysulfonebackbone with phenyl-ester-phenyl-aryl mesogen polysulfone backbone withphenyl-amide-phenyl mesogen polysulfone backbone withphenyl-amide-phenyl-cyano mesogen polysulfone backbone withphenyl-amide-phenyl-acyloxy mesogen polysulfone backbone withphenyl-amide-phenyl-alkyl mesogen polysulfone backbone withphenyl-amide-phenyl-aryl mesogen polysulfone backbone withphenyl-azo-phenyl mesogen polysulfone backbone withphenyl-azo-phenyl-cyano mesogen polysulfone backbone withphenyl-azo-phenyl-acyloxy mesogen polysulfone backbone withphenyl-azo-phenyl-alkyl mesogen polysulfone backbone withphenyl-azo-phenyl-aryl mesogen aromatic polysulfide backbone withphenyl-phenyl mesogen aromatic polysulfide backbone withphenyl-phenyl-cyano mesogen aromatic polysulfide backbone withphenyl-phenyl-acyloxy mesogen aromatic polysulfide backbone withphenyl-phenyl-alkyl mesogen aromatic polysulfide backbone withphenyl-phenyl-aryl mesogen aromatic polysulfide backbone with phenyl-Cdouble bond C-phenyl mesogen aromatic polysulfide backbone with phenyl-Cdouble bond C-phenyl- cyano mesogen aromatic polysulfide backbone withphenyl-C double bond C-phenyl- acyloxy mesogen aromatic polysulfidebackbone with phenyl-C double bond C-phenyl-alkyl mesogen aromaticpolysulfide backbone with phenyl-C double bond C-phenyl-aryl mesogenaromatic polysulfide backbone with phenyl-C triple bond C-phenyl mesogenaromatic polysulfide backbone with phenyl-C triple bond C-phenyl-cyanomesogen aromatic polysulfide backbone with phenyl-C triple bondC-phenyl- acyloxy mesogen aromatic polysulfide backbone with phenyl-Ctriple bond C-phenyl-alkyl mesogen aromatic polysulfide backbone withphenyl-C triple bond C-phenyl-aryl mesogen aromatic polysulfide backbonewith phenyl-ester-phenyl mesogen aromatic polysulfide backbone withphenyl-ester-phenyl-cyano mesogen aromatic polysulfide backbone withphenyl-ester-phenyl-acyloxy mesogen aromatic polysulfide backbone withphenyl-ester-phenyl-alkyl mesogen aromatic polysulfide backbone withphenyl-ester-phenyl-aryl mesogen aromatic polysulfide backbone withphenyl-amide-phenyl mesogen aromatic polysulfide backbone withphenyl-amide-phenyl-cyano mesogen aromatic polysulfide backbone withphenyl-amide-phenyl-acyloxy mesogen aromatic polysulfide backbone withphenyl-amide-phenyl-alkyl mesogen aromatic polysulfide backbone withphenyl-amide-phenyl-aryl mesogen aromatic polysulfide backbone withphenyl-azo-phenyl mesogen aromatic polysulfide backbone withphenyl-azo-phenyl-cyano mesogen aromatic polysulfide backbone withphenyl-azo-phenyl-acyloxy mesogen aromatic polysulfide backbone withphenyl-azo-phenyl-alkyl mesogen aromatic polysulfide backbone withphenyl-azo-phenyl-aryl mesogen polyarylene backbone with phenyl-phenylmesogen polyarylene backbone with phenyl-phenyl-cyano mesogenpolyarylene backbone with phenyl-phenyl-acyloxy mesogen polyarylenebackbone with phenyl-phenyl-alkyl mesogen polyarylene backbone withphenyl-phenyl-aryl mesogen polyarylene backbone with phenyl-C doublebond C-phenyl mesogen polyarylene backbone with phenyl-C double bondC-phenyl-cyano mesogen polyarylene backbone with phenyl-C double bondC-phenyl-acyloxy mesogen polyarylene backbone with phenyl-C double bondC-phenyl-alkyl mesogen polyarylene backbone with phenyl-C double bondC-phenyl-aryl mesogen polyarylene backbone with phenyl-C triple bondC-phenyl mesogen polyarylene backbone with phenyl-C triple bondC-phenyl-cyano mesogen polyarylene backbone with phenyl-C triple bondC-phenyl-acyloxy mesogen polyarylene backbone with phenyl-C triple bondC-phenyl-alkyl mesogen polyarylene backbone with phenyl-C triple bondC-phenyl-aryl mesogen polyarylene backbone with phenyl-ester-phenylmesogen polyarylene backbone with phenyl-ester-phenyl-cyano mesogenpolyarylene backbone with phenyl-ester-phenyl-acyloxy mesogenpolyarylene backbone with phenyl-ester-phenyl-alkyl mesogen polyarylenebackbone with phenyl-ester-phenyl-aryl mesogen polyarylene backbone withphenyl-amide-phenyl mesogen polyarylene backbone withphenyl-amide-phenyl-cyano mesogen polyarylene backbone withphenyl-amide-phenyl-acyloxy mesogen polyarylene backbone withphenyl-amide-phenyl-alkyl mesogen polyarylene backbone withphenyl-amide-phenyl-aryl mesogen polyarylene backbone withphenyl-azo-phenyl mesogen polyarylene backbone withphenyl-azo-phenyl-cyano mesogen polyarylene backbone withphenyl-azo-phenyl-acyloxy mesogen polyarylene backbone withphenyl-azo-phenyl-alkyl mesogen polyarylene backbone withphenyl-azo-phenyl-aryl mesogen aromatic polyester backbone withphenyl-phenyl mesogen aromatic polyester backbone withphenyl-phenyl-cyano mesogen aromatic polyester backbone withphenyl-phenyl-acyloxy mesogen aromatic polyester backbone withphenyl-phenyl-alkyl mesogen aromatic polyester backbone withphenyl-phenyl-aryl mesogen aromatic polyester backbone with phenyl-Cdouble bond C-phenyl mesogen aromatic polyester backbone with phenyl-Cdouble bond C-phenyl-cyano mesogen aromatic polyester backbone withphenyl-C double bond C-phenyl-acyloxy mesogen aromatic polyesterbackbone with phenyl-C double bond C-phenyl-alkyl mesogen aromaticpolyester backbone with phenyl-C double bond C-phenyl-aryl mesogenaromatic polyester backbone with phenyl-C triple bond C-phenyl mesogenaromatic polyester backbone with phenyl-C triple bond C-phenyl-cyanomesogen aromatic polyester backbone with phenyl-C triple bondC-phenyl-acyloxy mesogen aromatic polyester backbone with phenyl-Ctriple bond C-phenyl-alkyl mesogen aromatic polyester backbone withphenyl-C triple bond C-phenyl-aryl mesogen aromatic polyester backbonewith phenyl-ester-phenyl mesogen aromatic polyester backbone withphenyl-ester-phenyl-cyano mesogen aromatic polyester backbone withphenyl-ester-phenyl-acyloxy mesogen aromatic polyester backbone withphenyl-ester-phenyl-alkyl mesogen aromatic polyester backbone withphenyl-ester-phenyl-aryl mesogen aromatic polyester backbone withphenyl-amide-phenyl mesogen aromatic polyester backbone withphenyl-amide-phenyl-cyano mesogen aromatic polyester backbone withphenyl-amide-phenyl-acyloxy mesogen aromatic polyester backbone withphenyl-amide-phenyl-alkyl mesogen aromatic polyester backbone withphenyl-amide-phenyl-aryl mesogen aromatic polyester backbone withphenyl-azo-phenyl mesogen aromatic polyester backbone withphenyl-azo-phenyl-cyano mesogen aromatic polyester backbone withphenyl-azo-phenyl-acyloxy mesogen aromatic polyester backbone withphenyl-azo-phenyl-alkyl mesogen aromatic polyester backbone withphenyl-azo-phenyl-aryl mesogen aromatic polyamide backbone withphenyl-phenyl mesogen aromatic polyamide backbone withphenyl-phenyl-cyano mesogen aromatic polyamide backbone withphenyl-phenyl-acyloxy mesogen aromatic polyamide backbone withphenyl-phenyl-alkyl mesogen aromatic polyamide backbone withphenyl-phenyl-aryl mesogen aromatic polyamide backbone with phenyl-Cdouble bond C-phenyl mesogen aromatic polyamide backbone with phenyl-Cdouble bond C-phenyl-cyano mesogen aromatic polyamide backbone withphenyl-C double bond C-phenyl- acyloxy mesogen aromatic polyamidebackbone with phenyl-C double bond C-phenyl- alkyl mesogen aromaticpolyamide backbone with phenyl-C double bond C-phenyl-aryl mesogenaromatic polyamide backbone with phenyl-C triple bond C-phenyl mesogenaromatic polyamide backbone with phenyl-C triple bond C-phenyl-cyanomesogen aromatic polyamide backbone with phenyl-C triple bondC-phenyl-acyloxy mesogen aromatic polyamide backbone with phenyl-Ctriple bond C-phenyl-alkyl mesogen aromatic polyamide backbone withphenyl-C triple bond C-phenyl-aryl mesogen aromatic polyamide backbonewith phenyl-ester-phenyl mesogen aromatic polyamide backbone withphenyl-ester-phenyl-cyano mesogen aromatic polyamide backbone withphenyl-ester-phenyl-acyloxy mesogen aromatic polyamide backbone withphenyl-ester-phenyl-alkyl mesogen aromatic polyamide backbone withphenyl-ester-phenyl-aryl mesogen aromatic polyamide backbone withphenyl-amide-phenyl mesogen aromatic polyamide backbone withphenyl-amide-phenyl-cyano mesogen aromatic polyamide backbone withphenyl-amide-phenyl-acyloxy mesogen aromatic polyamide backbone withphenyl-amide-phenyl-alkyl mesogen aromatic polyamide backbone withphenyl-amide-phenyl-aryl mesogen aromatic polyamide backbone withphenyl-azo-phenyl mesogen aromatic polyamide backbone withphenyl-azo-phenyl-cyano mesogen aromatic polyamide backbone withphenyl-azo-phenyl-acyloxy mesogen aromatic polyamide backbone withphenyl-azo-phenyl-alkyl mesogen aromatic polyamide backbone withphenyl-azo-phenyl-aryl mesogen aromatic polycarbonate backbone withphenyl-phenyl mesogen aromatic polycarbonate backbone withphenyl-phenyl-cyano mesogen aromatic polycarbonate backbone withphenyl-phenyl-acyloxy mesogen aromatic polycarbonate backbone withphenyl-phenyl-alkyl mesogen aromatic polycarbonate backbone withphenyl-phenyl-aryl mesogen aromatic polycarbonate backbone with phenyl-Cdouble bond C-phenyl mesogen aromatic polycarbonate backbone withphenyl-C double bond C-phenyl- cyano mesogen aromatic polycarbonatebackbone with phenyl-C double bond C-phenyl- acyloxy mesogen aromaticpolycarbonate backbone with phenyl-C double bond C-phenyl- alkyl mesogenaromatic polycarbonate backbone with phenyl-C double bond C-phenyl- arylmesogen aromatic polycarbonate backbone with phenyl-C triple bondC-phenyl mesogen aromatic polycarbonate backbone with phenyl-C triplebond C-phenyl- cyano mesogen aromatic polycarbonate backbone withphenyl-C triple bond C-phenyl- acyloxy mesogen aromatic polycarbonatebackbone with phenyl-C triple bond C-phenyl- alkyl mesogen aromaticpolycarbonate backbone with phenyl-C triple bond C-phenyl-aryl mesogenaromatic polycarbonate backbone with phenyl-ester-phenyl mesogenaromatic polycarbonate backbone with phenyl-ester-phenyl-cyano mesogenaromatic polycarbonate backbone with phenyl-ester-phenyl-acyloxy mesogenaromatic polycarbonate backbone with phenyl-ester-phenyl-alkyl mesogenaromatic polycarbonate backbone with phenyl-ester-phenyl-aryl mesogenaromatic polycarbonate backbone with phenyl-amide-phenyl mesogenaromatic polycarbonate backbone with phenyl-amide-phenyl-cyano mesogenaromatic polycarbonate backbone with phenyl-amide-phenyl-acyloxy mesogenaromatic polycarbonate backbone with phenyl-amide-phenyl-alkyl mesogenaromatic polycarbonate backbone with phenyl-amide-phenyl-aryl mesogenaromatic polycarbonate backbone with phenyl-azo-phenyl mesogen aromaticpolycarbonate backbone with phenyl-azo-phenyl-cyano mesogen aromaticpolycarbonate backbone with phenyl-azo-phenyl-acyloxy mesogen aromaticpolycarbonate backbone with phenyl-azo-phenyl-alkyl mesogen aromaticpolycarbonate backbone with phenyl-azo-phenyl-aryl mesogen

1. A waveplate comprising a mesogen-containing polymer film having a backbone and having sidechains containing mesogen groups, wherein the mesogen-containing polymer film has a length, a width, and a thickness such that said mesogen-containing polymer film is insertable into a channel in an optical pathway of the planar lightwave circuit.
 2. A waveplate according to claim 1 wherein said mesogen-containing polymer film has a birefringence sufficiently high to rotate or convert a polarization state of an optical signal traversing the optical pathway.
 3. A waveplate according to claim 2 wherein the birefringence is at least 0.52.
 4. A waveplate according to claim 2 wherein the waveplate is a half waveplate of thickness between 5 and 25 μm.
 5. A waveplate according to claim 2 wherein the waveplate is a quarter waveplate of thickness between 5 and 25 μm.
 6. A waveplate according to claim 1 wherein the mesogen-containing polymer film is formed of a polymer having a glass transition temperature between 100 C and 300 C.
 7. A waveplate according to claim 1 wherein the backbone contains monomers having at least two groups that provide rotational freedom within the backbone.
 8. A waveplate according to claim 1 wherein the waveplate has a warpage of less than 350 μm.
 9. A waveplate according to claim 1 wherein the backbone comprises a polymer selected from the group consisting of: polyimides, polyetherimides, polyesterimides, polyamideimides, polyketones, polyarylethers, polyetherketones, polysulfones, polysulfides, polyarylenes, polyesters, polyamides, polycarbonates, polyolefins, polyvinylesters, polyurethanes, polyacrylates, polyphenylenes.
 10. A waveplate according to claim 9 wherein the backbone comprises polyetherimide polymer.
 11. A waveplate according to claim 10 wherein the backbone is formed of one or more components selected from the group consisting of 4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride); 4,4′-(hexafluoroisopropylidene) diphthalic anhydride; 2,2′-bis(trifluoromethyl)benzidine; and bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate.
 12. A waveplate according to claim 10 wherein the mesogen group is biphenyl.
 13. A waveplate according to claim 12 wherein the side chains further comprise spacing groups linking the mesogen groups to the linking groups, the spacing groups being selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 14. A waveplate according to claim 9 wherein the backbone comprises polyamide polymer.
 15. A waveplate according to claim 14 wherein the backbone is formed of one or more components selected from the group consisting of isophthalic chloride; 2,2′-bis(trifluoromethyl)benzidine; bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate; and 4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride).
 16. A waveplate according to claim 15 wherein the backbone is formed of isophthalic chloride; 2,2′-bis(trifluoromethyl)benzidine; and bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate.
 17. A waveplate according to claim 15 wherein the backbone is formed of 2,2′-bis(trifluoromethyl)benzidine; bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate; and 4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride).
 18. A waveplate according to claim 14 wherein the mesogen group is biphenyl.
 19. A waveplate according to claim 18 wherein the side chains further comprise spacing groups linking the mesogen groups to the linking groups, the spacing groups being selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 20. A waveplate according to claim 9 wherein the mesogen groups have the form phenyl-X-phenyl-R or phenyl-phenyl-R, where X is selected from the group consisting of azo, diazo, azoxy, nitrone, carbon-carbon double bond, carbon-carbon triple bond, amide, imide, Schiff base, and ester; and R is selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 21. A waveplate according to claim 9 wherein the mesogen groups are selected from the group consisting of trans 1,3 cyclohexane; trans 1,4 cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5 disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.
 22. A waveplate according to claim 9 wherein the mesogen group is biphenyl.
 23. A waveplate according to claim 9 wherein the side chains comprise linking groups linking the mesogen groups to the backbone, wherein the linking groups are selected from the group consisting of ether, ester, amide, imide, urethane, alkylene, alkyl.
 24. A waveplate according to claim 1 wherein the mesogen groups have the form phenyl-X-phenyl-R or phenyl-phenyl-R, where X is selected from the group consisting of azo, diazo, azoxy, nitrone, carbon-carbon double bond, carbon-carbon triple bond, amide, imide, Schiff base, and ester; and R is selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 25. A waveplate according to claim 24 wherein the side chains comprise linking groups linking the mesogen groups to the backbone, wherein the linking groups are selected from the group consisting of ether, ester, amide, imide, urethane, alkylene, alkyl.
 26. A waveplate according to claim 24 wherein the side chains further comprise spacing groups linking the mesogen groups to the linking groups, the spacing groups being selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 27. A waveplate according to claim 1 wherein the mesogen groups are selected from the group consisting of trans 1,3 cyclohexane; trans 1,4 cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5 disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.
 28. A waveplate according to claim 27 wherein the side chains comprise linking groups linking the mesogen groups to the backbone, wherein the linking groups are selected from the group consisting of ether, ester, amide, imide, urethane, alkylene, alkyl.
 29. A waveplate according to claim 28 wherein the side chains further comprise spacing groups linking the mesogen groups to the linking groups, the spacing groups being selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 30. A waveplate according to claim 27 wherein the side chains further comprise spacing groups linking the mesogen groups to the linking groups, the spacing groups being selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 31. A waveplate according to claim 1 wherein the mesogen group is biphenyl.
 32. A waveplate according to claim 31 wherein the side chains further comprise spacing groups linking the mesogen groups to the linking groups, the spacing groups being selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 33. A waveplate according to claim 1 wherein the mesogen groups comprise at least two aromatic groups and wherein the mesogen groups associate to help maintain birefringence as the film is drawn.
 34. A waveplate according to claim 33 wherein the side chains further comprise spacing groups linking the mesogen groups to the linking groups, the spacing groups being selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 35. A waveplate according to claim 1 wherein the side chains comprise linking groups linking the mesogen groups to the backbone, wherein the linking groups are selected from the group consisting of: ether, ester, amide, imide, urethane, alkylene, alkyl.
 36. A waveplate according to claim 1 wherein the side chains further comprise spacing groups linking the mesogen groups to the linking groups, the spacing groups being selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 37. A waveplate according to claim 9 wherein the side chains further comprise spacing groups linking the mesogen groups to the linking groups, the spacing groups being selected from the group consisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 38. A waveplate according to claim 1 wherein the spacing groups are sufficiently long and sufficiently flexible to allow the mesogens of adjacent sidechains to associate as a film of the mesogen-containing polymer is stretched.
 39. A planar lightwave circuit comprising a waveguide and a waveplate according to any of claims 1, 2, 3, 7, 8, 10, 14, 11, 15, 20, 31, 33, 23, and 36 positioned in an optical pathway of the waveguide.
 40. A planar lightwave circuit according to claim 39 wherein the waveguide is one of a plurality of waveguides of an arrayed waveguide grating positioned between two free propagation regions of the planar lightwave circuit, and wherein the waveplate is positioned in an optical pathway of each of the plurality of waveguides of the arrayed waveguide grating.
 41. A planar lightwave circuit according to claim 39 wherein the waveplate is positioned at an angle to the waveguides that reduces back reflection caused by the waveplate groove, glue, and waveplate. 